THE MENU Double mushroom soup Roast fresh ham Cumberland Turnip mousseline Pureed spinach with croutons Caramel-glazed mocha cream puffs

NOTHING IS NICER than having friends for dinner on the Saturday after Thanksgiving, especially if you've been invited out for Thanksgiving Day itself. But guest lists invariably get out of hand this time of year, what with friends having households full of out-of-town visitors or grown children returned home and suddenly civilized. It is all too easy to ask more people than can possibly fit around the table. The solution, of course, is the buffet dinner.

This meal can go far to restore the buffet dinner's good name, which has been assaulted over the years by tired, cold dishes and main courses with more mush than interest, the better to be consumed without benefit of a knife. Here we start with a soup of fresh mushrooms reinforced with dried Italian or Polish mushrooms, perfumed with a good dry sherry and served in manageable mugs. The main course is a festive fresh ham or, as some prefer to call it, leg of pork, glazed with the makings of a Cumberland sauce which then forms the basis of the gravy. The meat, cooked to a succulent tenderness, is carved thinly so that while a knife can be put to good use by guests who are expert lap jugglers, it is not necessary. Accompanying the fresh ham and embellishing the dinner plates with good color and complementary flavors are an airy turnip mousseline and pure'ed spinach garnished with fresh, buttery croutons. Dessert is the best of finger foods -- little cream puffs glazed with caramel and filled with a mocha cream.

Most of this meal can be made in advance, a boon at all times and especially so when large numbers are involved. The mushroom soup can be completely assembled the day before and only the sherry added just before the soup is heated and served. The dried wild Italian porcini mushrooms, with their heady earthy flavor, are worth searching out. They are sold in 1 3/4-ounce packets in Italian markets as well as in some specialty food stores. Dried Polish mushrooms are also very good. If finding either of these is too difficult, ordinary dried mushrooms, which many supermarkets sell in plastic cups, can be substituted.

It would be a mistake to count on picking up a fresh ham on the day you want to cook it, but most supermarkets are only too happy to order these for customers. About five days' advance notice is required, so plan accordingly. The meat is basted during its last hour of cooking with Cumberland sauce, a splendid English invention consisting of red currant jelly, ruby port (the least expen- See DINNER, F10, Col. 1 FRESH HAM DINNER, From F1 sive, most ordinary red port will do nicely), orange juice, lemon juice and mace. Cumberland sauce is more usually served cold as an accompaniment to ham, pork and meat pies. Basting the fresh ham with it gives the meat a lovely color and the gravy a rich tartness. The fresh ham needs long, slow cooking -- up to five hours, depending on its weight -- so count backwards carefully to make sure it gets into the oven on time. Plan to have the ham finished a good 40 minutes before it is to be carved. It needs time to settle and will stay warm under a tent of foil. This also lets you raise the oven's temperature and bake the turnip mousseline.

I cooked turnips for the mousseline three different ways in the hope that one would result in a drier end product. It made no difference whether the turnips were boiled, steamed or even baked. The pure'e that was made from them was in each case full of liquid, so I suggest the easiest way, boiling. The turnips must be cooked far enough in advance for the pure'e to be turned into a strainer and the excess liquid drained off. The cinnamon is almost imperceptible but adds a lovely dimension to the turnips. The dish is very delicate and not at all what non-turnip lovers would expect.

The spinach can also be made the day before, with the final five minutes of cooking occurring just before it is served. While fresh spinach is always preferable, I myself draw the line at hauling, cleaning and cooking the eight or 10 pounds I would need for 16 people. Considering the alternative, compromising with frozen spinach is perfectly acceptable. The spinach should be removed from the freezer about two or three hours before you plan to work with it since it must be partially thawed, a process that always takes longer than one thinks.

The bother about making cream puffs used to be the arm energy involved in beating the eggs into the cooked paste base. The food processor is easy and fast and the results are excellent. The recipe here is double the one I ordinarily use. It fills the smallest processor bowl more than I would like for comfort, but nevertheless it works. I always plan to make the double recipe since leftover puff shells keep beautifully in the freezer. Having them in reserve is money in the bank, especially for those times when the prospect of making yet another dessert is unbearable. The shells can be filled with pastry cream as well as with whipped cream. According to Bernard Clayton, the expert on bread and pastrymaking, bread flour makes the puffiest shells. The 14-inch pastry bag holds the entire double batch, which avoids having to refill a bag that wants only to cling to itself after a first batch has been squeezed out of it. Large pastry bags come either in a heavy canvas with a plastic coating inside or in a lightweight nylon. I prefer the latter, which is made in France and carries the "Imper" label. Both types are washable, and having two is better than one, although the thin nylon bag dries very quickly. They can be found at most good kitchenware stores.

Needless to say, these recipes, with the exception of the fresh ham, can be halved for a terrific dinner for eight.

DOUBLE MUSHROOM SOUP (16 servings) 1 1/2 ounces dried wild Italian mushrooms (porcini) or dried Polish mushrooms, or ordinary dried mushrooms sold in cups in supermarkets 10 tablespoons (1 stick plus 2 tablespoons) butter 3 pounds mushrooms, cleaned and sliced 4 large onions, sliced 2 10 3/4-ounce cans condensed chicken broth 6 cups milk 2 cups heavy cream Salt and pepper to taste 1 cup full-bodied dry sherry, such as Dry Sack

Rinse the dried mushrooms quickly under warm running water, place them in a bowl and pour boiling water over them to cover. Set aside while you make the soup.

Melt the butter to foaming in a large saute' pan, add the mushrooms and cook, stirring, until the mushrooms first give out liquid and then the liquid cooks off. Add the onions and cook over low heat until the onions are soft and transparent. Do not let them color. Turn the mixture into a processor with the steel blade, and with the motor running add half the chicken broth. Process until the mushrooms are reduced to a pure'e. Turn the pure'e into a large pan and add the remaining chicken broth along with the milk and cream. Strain the liquid from the dried mushrooms through four layers of damp cheesecloth and add the liquid to the pan. Shred the softened dried mushrooms and add. Season with salt and pepper. Just before serving, add the sherry and beat. Serve in mugs or bowls.

ROAST FRESH HAM CUMBERLAND (16 servings) 10- to 12-pound whole fresh ham, rind removed Salt and pepper 10-ounce jar red currant jelly 1 cup ruby port 1/2 cup orange juice 1/4 cup lemon juice 1/4 teaspoon ground mace 1 cup chicken broth 1 cup beef bouillon

Rub the fresh ham with salt and pepper and roast it in a large pan at 325 degrees for 25 minutes per pound.

Combine the red currant jelly, port, orange juice, lemon juice and mace and heat until the jelly is melted. Use this to baste the meat frequently during its last hour of cooking. If during this last hour the fresh ham is not browning sufficiently, raise the oven temperature to 400 degrees. If it is browning too quickly, cover the meat with a tent of foil.

The ham is cooked when its internal temperature reads 165 degrees. Let the cooked ham settle under a tent foil on a carving board while you make the sauce. Skim off as much fat as possible from the pan juices, add the chicken broth and beef bouillon and bring to the boil while stirring with a wooden spoon and scraping up any brown bits that stick to the pan. Carve the ham, arrange on a platter and serve the sauce separately.

TURNIP MOUSSELINE (16 servings) 6 pounds medium-large turnips 12 tablespoons butter 1 cup heavy cream 1/4 teaspoon cinnamon 1/2 teaspoon sugar Salt and pepper to taste 8 eggs, separated 1/2 cup melted butter

Cook the turnips either the day before or the morning of the evening the mousseline is to be made. Peel the turnips, cut them into thick slices and cook in boiling salted water for about 20 minutes, or until the turnips are tender. Turn them into a colander, drain well and pure'e them in a food processor or put them through a food mill. Turn the pure'e, which will be very liquid, into a large fine-meshed strainer and set over a bowl. Pour off the liquid as it accumulates, something it will do rather quickly at first, and then place the strainer with pure'e plus bowl in the refrigerator. Leave to drain either overnight or for several hours.

Turn the drained pure'e into a heavy saucepan, place it over high heat and, stirring constantly, heat the pure'e for about 5 minutes. Remove from heat and beat in the butter, cream, cinnamon, sugar and salt and pepper. Then beat in the eggs yolks, one at a time. The mixture can be prepared several hours in advance up to this point. About 45 minutes before serving, beat the egg whites until they are stiff but not dry. Fold the whites into the turnip mixture and pile into a 15-inch oval gratin dish which has been brushed with some of the melted butter or in two 9- or 10-inch round ovenproof dishes suitable for serving. Brush the mixture with the rest of the melted butter. Bake in a 400-degree oven for 1/2 hour, or until the mousseline is nicely browned and puffed.

PUREED SPINACH WITH CROUTONS (16 servings) 8 10-ounce packages frozen leaf spinach, partially defrosted 1/2 pound butter plus 4 tablespoons 3 tablespoons minced shallots Salt and pepper to taste 6 slices firm-textured white bread

Cut the partially thawed spinach into 1-inch cubes, place in a large pan, bring to a boil and cook, covered, for 5 minutes over moderately high heat, stirring once or twice. Turn the spinach into a colander and let it drain while it cools. When it is cool enough to handle, squeeze it, in small handfuls, as dry as possible. In two batches, pure'e it in a food processor.

Melt the 1/2 pound butter in a saucepan, add the minced shallots and cook over low heat for about 5 minutes, or until the shallots are transparent and soft. Add the pure'ed spinach, season with salt and pepper and cook over low heat, stirring constantly, for 5 minutes. Turn the pure'e into a serving dish and garnish with the croutons.

The croutons can be made several hours in advance. Remove the crusts from the bread and cut the bread into 1/2-inch cubes. Melt 4 tablespoons butter in a large frying pan and toss the cubes in it until they are golden brown on all sides.

CARAMEL GLAZED MOCHA CREAM PUFFS (Makes about 60 1 1/2- to 2-inch puffs) For the cream puff shells: Softened butter to grease two baking sheets 1 cup water 14 tablespoons (1 stick plus 6 tablespoons) unsalted butter 1 cup milk 1 1/2 teaspoons salt 2 teaspoons sugar (omit for cream puffs with savory fillings) 2 cups bread flour or unbleached flour 8 large eggs For the caramel glaze: 1 1/2 cups sugar 6 tablespoons water For the filling: 2 1/2 cups heavy cream 1/2 cup confectioners' sugar 4 tablespoons unsweetened cocoa, preferably Dutch 2 tablespoons instant espresso coffee powder 2 tablespoons dark rum

Line two large baking sheets with foil and grease the foil with softened butter. Set aside.

To make the cream puff shells, combine the water, butter, milk, salt and sugar in a heavy pan and bring slowly to a full boil, stirring constantly with a wooden spoon. Remove from heat, add all the flour at once and beat, off heat, with a wooden spoon until the mixture comes away from the sides and forms a ball. Return to heat and dry out the paste by mashing the mixture down onto the bottom of the pan with the wooden spoon and bringing it up and folding it over, much as if you were kneading bread. Continue for 3 to 5 minutes, or until a sandy-looking film of paste forms on the bottom of the pan. Remove from heat and let the paste stand for about 15 minutes, beating it occasionally as it cools. Turn the paste into a food processor with the steel blade and, with the motor running, add, one after the other, the eggs. Process about 15 seconds more after the last egg is added.

Fit a pastry bag, preferably one 14 inches long, with a plain tube with a 1/2-inch opening, twist the bottom of the bag into the tube, place the bag in a bowl and spoon the paste into the bag. Untwist the end and push the paste down from the top. Hold the tube steady about 1/2 inch above the baking sheet and squeeze out mounds about 1 1/2 inches in diameter, allowing the paste to push up around the tip of the tube. Withdraw the tube and continue to make mounds about 2 inches apart. If any of the mounds have pointy tops, pat these down with a finger moistened with cold water.

Place the filled baking sheets in a 400-degree oven. In no case open the oven door before the shells have baked for at least 15 minutes. It is safer to check after 20 minutes and again 5 minutes later. Bake the shells 25 to 30 minutes, or until they are puffed and browned. Remove from the oven and with a long, thin knife, make a slit near the bottom to let out any steam.

The shells can be made the day before and stored overnight in tightly closed plastic bags, or they can be made well in advance and frozen while they are still warm. To thaw and recrisp frozen shells, place them, unthawed, in a 375-degree oven for 8 to 10 minutes.

Glaze the unfilled shells with caramel the day they are to be eaten. To make the caramel, place the sugar in a heavy saucepan and shake the pan to make an even layer of sugar on the bottom. Then add the water carefully so that none of the sugar splashes onto the sides of the pan. Place over low heat and cook until the sugar melts. Do not stir. When the sugar begins to color, shake the pan gently so that the sugar colors evenly. Remove the pan from heat before the caramel is the rich golden brown it should be since it will continue to cook off heat. Working quickly and holding the puff shells by the bottom, dip the tops into the caramel and set the shells aside. When the caramel hardens, and about four or five hours before the puffs are to be eaten, fill the shells with the mocha cream.

Whip the cream with the confectioners' sugar until it begins to thicken. Add the cocoa and instant espresso coffee and continue to beat until the cream is very stiff. Then quickly beat in the rum. Fill a pastry bag fitted with a plain or star tube with a 1/8-inch opening. Slit the shells in half and pipe the cream into the hollows. Put the puffs back together, arrange on a platter and refrigerate until needed.