THERE ARE NO two ways about it, spinach is the dirtiest vegetable we normally cook. And, unfortunately, of the three ways in which this richly colored and flavored green is generally packaged, the best -- loose leaves -- is the worst in terms of dirt.

So, when using such spinach it is important to remember that it only takes a few grains of sand in a spinach souffle' to ruin the whole meal for one of your guests. But bulk spinach also has the best leaves for salads and the finest taste of the three types of spinach available in most markets.

To clean spinach, first tear off the thick stems. Fill the sink with cold tap water and add the spinach. Shake it around to dislodge the dirt, then just leave it alone for a few minutes so the sand can settle to the bottom of the sink while the leaves float on top. Repeat the procedure at least three times, until there is absolutely no sand left in the sink.

When picking out bulk spinach, look for well developed, crisp, dark green leaves. Avoid any that are pale in color, moist or wilted.

Raw spinach leaves are also sold in plastic packages. There is little problem with dirt here -- the spinach has been thrice rinsed in spring water. But the quality of the leaves and their freshness is often poorer than that of bulk spinach. Use these plastic-wrapped prerinsed leaves when you are in a hurry, when the spinach is to be chopped, pure'ed, creamed, saute'ed or baked, and when a clean, deep, rich spinach taste isn't critical.

Unwrap and carefully pick through the spinach. Discard leaves that are yellow or wet and remove the tough, thick stems. One quick rinse in cold water to refresh the leaves is a good idea. Always use packaged spinach as soon as possible after purchasing, as the sealed environment causes the spinach to deteriorate quickly.

The third way we find spinach is frozen. A 10-ounce package is roughly equivalent to a pound of fresh spinach. Frozen spinach should be defrosted as slowly as possible (two days in the refrigerator is ideal) and then you should separate the leaves and pick out the thick stems. Squeeze as much liquid as you can from frozen spinach before using it. Frozen spinach is good for pure'es, creamed spinach, spinach souffle's -- basically any recipe that requires chopped or pure'ed spinach to be further cooked.

As frozen spinach is already cooked and wilted as much as it needs to be, do not even think about heating frozen spinach to defrost it or it will become an insipid dark green mess.

To steam or wilt spinach -- clean the leaves, remove from the water and shake as dry as possible. A good shaking is all that is necessary; don't bother with a salad spinner. Place the leaves in a large pot, a stockpot is good for this as there is plenty of room to turn the spinach so that it cooks evenly without leaves flying out onto the stove.

Place the pot over medium high heat and cover. Cook for a minute or so, then stir the leaves from the top down to the bottom. Repeat this procedure two or three times until all the leaves have just wilted down -- not until they have overcooked into gray-green, wet muck. Immediately remove from the heat and drain. The spinach will have given off a lot of liquid.

At this point, depending on the recipe, you might want to season the spinach with a little salt (or a few drops of lemon juice if not using salt), freshly ground black pepper and some freshly grated nutmeg. A pound of loose leaves reduces to about 1 1/2 cups, or 3-4 servings.

From the simplest recipe for spinach, wilted or steamed as just described, and flavored with just a little salt, pepper and nutmeg, spinach can be turned into some quite grand dishes, as well as some old-time favorites.

The first recipe below is for spinach noodles, which become fettucine alfredo prepared in its purest and most classical way -- the simplest, richest, and easiest version of alfredo you will ever make. The recipe is followed by a variation of Fettucine With Saffron Cream that is grand, splendid, and quite expensive -- so save it for a very special time. Next is a simple, flourless and thus very light, hot spinach souffle' made in individual ramekins -- a technique that makes souffle' all but infallible.

Warm salads are a fairly recent addition to American cooking, and the example here is a fine one full of understandable tastes put together with a slightly different twist. It makes a great beginning to a slightly adventurous meal. The warm salad is followed by a very traditional Indian vegetable preparation, a spicy combination of stewed spinach flavored with fresh ginger root and garlic and combined with baby new potatoes -- or any waxy potato can be used, just cut the cooked potatoes into large bite-sized pieces before adding to the spinach.

From San Francisco's famous Italian restaurant, Vanessi, comes a hearty frittata made with spinach and ground beef. Perfect for brunch or a light dinner. This frittata is also good served at room temperature, so you can make it a few hours ahead and store it on a plate covered with plastic wrap in a cool spot.

Finally, from one of the great young French chefs comes a spectacular nouvelle-style dish: Finnan Haddie Mousse wrapped in spinach and accompanied by a mustard hollandaise. A lot of work, but well worth the effort when you have the time. SPINACH FETTUCINE ALFREDO (2-4 servings) 1/2 pound fresh spinach 1 1/2 cups all-purpose flour 1 extra large egg For the sauce: 1 cup whipping cream 4 tablespoons unsalted butter Salt Freshly ground black pepper Ground white pepper Freshly grated nutmeg 4-5 rounded tablespoons freshly grated parmesan

Clean and steam the spinach. Squeeze hard to remove as much moisture as possible. Pure'e in a food processor, then add the remaining ingredients and process until a ball of dough forms. The dough should be dry but still maleable. If too moist, add a tablespoon or so of additional flour and process until incorporated. Let the ball bounce around on top of the blades for about 30 seconds after it forms, then remove and set aside to rest for 10-15 minutes before rolling out.

Roll out the dough in a pasta machine, then cut into strips to make fettucine, or whatever.

Combine the cream and butter in a saucepan and reduce over medium heat to about 1/2 cup. Season with salt, both black and white pepper, and generously with nutmeg. Simmer for another minute or two.

Just before serving, cook the pasta al dente in lots of boiling water -- it will only take about a minute and a half. While the pasta is cooking, stir the cheese into the cream and adjust the seasonings. Drain the cooked pasta quickly and thoroughly and toss with the cream sauce.

Serve immediately with extra parmesan passed separately.

Variation -- Fettucine With Saffron Cream: Substitute 2 generous teaspoons of saffron threads for the white pepper and nutmeg. Serve with simply prepared meats -- poached or baked fish, roast chicken, or grilled lamb or veal chops. HOT SPINACH SOUFFLE (4 servings) 2 tablespoons butter 1 1/2 pounds fresh spinach, cleaned 2 tablespoons whipping cream Salt Freshly ground black pepper Nutmeg 6 extra-large eggs

Melt the butter in a large heavy-bottomed saucepan and add the spinach. Cook until spinach has wilted and most of the moisture has evaporated. Add the cream and cook again until most of the moisture is gone -- about 8 minutes. Season with salt, pepper and nutmeg. Pure'e with 4 egg yolks (save the remaining yolks for another use).

Beat the whites until stiff. Stir about a quarter of the beaten whites into the spinach mixture to lighten it. Gently fold in the remaining whites. Pour into 4 individual white ramekins, which have been buttered and floured.

Bake at 400 degrees for 10-12 minutes. Serve at once. WARM SALAD OF FRESH SPINACH, CHICKEN LIVERS, BACON AND MUSHROOMS (4 servings) 3/4 pound cleaned fresh spinach leaves 3 slices bacon 1 tablespoon unsalted butter 3 large mushrooms 6 ounces chicken livers 1/3 cup olive oil 2 tablespoons red wine vinegar 1 teaspoon spicy dijon mustard Salt Freshly ground black pepper

Make sure the spinach is thoroughly cleaned and dried. Place in a large flat serving plate and set aside in a cool spot.

Cut the bacon into small strips and saute' until crisp. Remove the bacon and keep warm. Drain off all but a tablespoon or so of the fat. Add the butter to the pan.

Remove the stems from the mushrooms and cut into julienne strips, either by hand or with a mandoline. Saute' the mushrooms in the fat and butter mixture over high heat for a minute or so, then drain and combine with the bacon. Keep warm.

Saute' the livers in the remaining fat and butter until nicely browned on the outside but still a little pink in the center. Cut into half-inch pieces. Keep warm.

Combine the oil, vinegar and mustard and heat to lukewarm.

Arrange the livers on the spinach, sprinkle with the bacon and mushrooms and dress with the warm vinaigrette. Season with salt and pepper to taste and serve at once. SPINACH WITH GINGER AND NEW POTATOES (4 servings) 4 tablespoons unsalted butter 1 inch piece of fresh ginger root 2-3 garlic cloves Cayenne, to taste 1 pound fresh spinach, cleaned Juice of 1 lemon Salt Freshly ground black pepper 12-16 very small new potatoes, boiled in their jackets until just barely tender

Melt the butter in a large saucepan. Pure'e ginger with garlic in a food processor and add to the butter. Saute' for 2 minutes, then add a few dashes of cayenne (depending on how hot you want the dish) and the spinach. Cook until spinach is wilted, then add the lemon juice and season with salt and freshly ground black pepper. Cook for 8 to 10 minutes, gently, until the spinach has developed the full flavor of the ginger and garlic and become a dark green.

Stir in the new potatoes and cook until potatoes are heated through. Serve at once. VANESSI'S SPINACH FRITTATA (4 servings) 1 pound fresh spinach 1 medium onion, finely chopped 2 garlic cloves, finely chopped 1/3 cup olive oil 1 pound lean ground beef 6 eggs Salt Freshly ground black pepper

Clean and steam the spinach as described above. Squeeze as much moisture as you can out of the spinach, then chop somewhat coarsely.

Saute' the onion and garlic in the olive oil, preferably in a nonstick saute' pan, until tender and translucent. Add the beef and brown evenly, breaking up any large pieces of the beef that have clung together.

Beat the eggs with a little salt and pepper and pour over the meat mixture. Reduce the heat to low and cook until the eggs are almost set, then sprinkle the chopped spinach over the top and place under the broiler until the eggs are set and the top of the frittata is lightly browned. Slide it out of the pan onto a serving plate. Cut into wedges. JEAN-JACQUES JOUTEUX'S FINNAN HADDIE MOUSSE WRAPPED IN SPINACH LEAVES WITH MUSTARD HOLLANDAISE (Les Semailles Restaurant) (6 servings) 1 pound fresh spinach (choose the largest leaves you can find) 1 pound finnan haddie cut into cubes, or 1 pound cleaned raw shrimp 2 eggs 1/4 cup cream 1/2 cup finely chopped fresh chives, or half chives and half fresh basil Salt Freshly ground black pepper Mustard hollandaise (recipe follows)

Clean the spinach, then blanch the leaves, 2 or 3 at a time, in boiling water for 20-30 seconds. Carefully transfer to a bowl of ice water. Repeat with the remaining spinach. Carefully and patiently line the inside of 6 individual (3-inch diameter) ceramic ramekins.

Place the fish in a food processor and pure'e. Add the eggs and pure'e for another 30 seconds, then pour the cream into the fish mixture in a thin stream while still processing. Remove from the processor, press through a strainer and stir in the herbs. Season with salt and freshly ground black pepper to taste. Spoon into the prepared molds. Dip your fingers into cold water and smooth the top of the mousses. Cover with remaining spinach leaves (there may be some left over). Place in a water bath and bake at 425 degrees for 12 minutes. While the mousses are cooking, prepare the hollandaise. MUSTARD HOLLANDAISE 1 pound unsalted butter 2 eggs plus 1 yolk 1/2 teaspoon dry mustard 1 teaspoon dijon or meaux mustard Salt Freshly ground black pepper 2-3 tablespoons freshly squeezed lemon juice A little hot water, if necessary Melt the butter in a small saucepan and bring it to a boil. Meanwhile, combine the eggs and egg yolk, mustards, a little salt and pepper in a food processor and process for 60 seconds.

When the butter reaches a boil, slowly pour it into the egg and mustard mixture, while still processing. When all the butter has been incorporated, add the lemon juice and adjust the seasoning. If too thick, thin with a little hot water.

Unmold the mousses and pour the sauce around them. Serve at once.