SUE SPITLER nibbled through a slice of lemon-glazed yam bread, dug into a brandy-sauced yam casserole, then plunged a fork into a yam-topped meat loaf, fragrant with basil.

It had been yam day -- yam week, in fact -- for Spitler, a food consultant who creates recipes for a living. On assignment of Southern Living, she was at work on canned yam recipes for the magazine's traveling cooking school.

Leslee Reis also creates recipes for a living, inventing dishes like pike mousseline with baby shrimp and buerre blanc, or scallops on puff pastry with fresh spinach and sauce nantais. These she serves to customers in her suburban Chicago resturant, Cafe Provencal.

Alma Lach is an author and teacher who has created recipes for her exhaustive volume on French cuisine, "The Hows and Whys of French Cooking," for her classes, for the public television program, "Over Easy," and for a book on Chinese cooking, her current project.

To those cooks who follow "Joy of Cooking" by rote, for fear of ruining some perfectly good groceries, or worse, incurring the wrath of a hungry family or the disappointment of dinner guests, professional experimenters like Spitler, Reis and Lach may seem as amazing as Edison in his laboratory.

Sue Spitler is the first to admit she wouldn't be in business without her 200 or so cookbooks. Yet she couldn't do her job if she didn't know by heart how to do a basic bechamel, whip up a souffle or make classic puff paste.

Formerly the food editor of Sphere (now Cuisine) magazine, where the receipes were often classic French or ethnic, Spitler is now a freelancer who specializes in convenience recipes. She has had to come up with as many as 40 fast dishes using the same main ingredient -- such as canned yams.

In the kind of overwhelming project, Spitler brainstorms the topic at hand -- yams -- then methodically lists her ideas: combinations both traditional (yams with molasses, orange juice, sweet sherry or marshmallows), and no so traditional (yams in a souffle with a mild cheese, or yams with chicken). Then she organizes her ideas into categories: entrees, soups, breads, vegetable dishes, desserts.

Next, she scans her books to see what's already been done.

"About 10 percent of what I do is genuinely original," said Spitler. "The rest of the recipes are adaptations. You think you have a brilliant idea, and you find it two days later in a cookbook. So you throw it out and start over."

(Spitler is especially sensitive to the problem of stealing receipes. When she was food editor at Spheres, a few respected Chicago freelancers submitted recipes the staff discovered had been lifted verbatim from James Beard and Time-Life cookbooks. Thereafter freelancers were required to sign a statement declaring their recipes were entirely original. Or, if the recipes were adaptations, the freelancer was asked to supply published sources, and show that at least three ingredients, as well as techniques, were changed.)

On a good day, Spitler and her assistant turn out winners on the first try. On a bad day, she gives up after a recipe fails three times in a row.

"Acturally yams have been pretty east," said Spitler. "Pudding and pie filling mixes are a different story. Their composition is so balanced that almost anyting you add makes them break down, and then the stuff won't stiffen.

"So what can you do with chocolate pudding, besides make a pie or a parfait? For one recipe, I finally added some ornage extract, topped the pudding with brown sugar and treated it like creme brulee."

Some of the other products Spitler has built recipes around include syrup, soy sauce, "ball park" mustard and grape juice.

Like Spitler, Leslee Reiss also dream up new dishes. With her creations, Reis tries to please 100 guests each night in her panaled, pink-linened restaurant in Evanston, Ill.

Reis' cooking career began with her mother's pre-wedding advice: "Buy your meat from a butcher."

She was in school at the time, studying biochemistry at Harvard, and selected the best she could find -- the meatman used by Julia Child. Through him, she met Child, and plunged into French cooking -- or what was left of it -- washing dishes on Child's Boston-based TV program.

After study at the Cordon Bleu in Paris, she returned to Chicago where she ran a catering service and then opened her own restaurant.

Reis has four basic menus, plus daily specials, that change with the season. She sometimes uses a process of elimination in creating a new entree. Her scallops with fresh spinach and chives, served on puff pastry with sauce nantais, is a case in point.

"I decided first on the scallops because shrimp is boring, lobster is even more expensive, and we'd just done crabs. I love fresh chives and they were in season and available, so they went in.Spinach was also fresh and plentiful, and I like it with scallops, so that was added. I still needed a sauce and a starch. I had been looking for a way to use a sauce I learned to do last summer in France -- buerre nantais, which is almost like a mayonnaise -- a sort of buerre blanc with heavy cream. And for the starch, I decided to use puff paste, which is light and more interesting than potatoes. I had made all these various parts, so to create the dish, I just put them together."

Reis freely admits she gets ideas from other chefs. In fact, she spends at least one week a year working about 15 hours a day in a French kitchen, and another week or so eating her way through Michelin-rated restaurants.

Michel Guerard's smoked lotte (bellyfish) served en croute inspired Reis' smoked sturgeon served atop squares of puff paste. "Guerard's preparation was wonderful, but I don't like dishes wrapped in pastry. They taste soggy." w

Actually, it was soggy starch that made, rather than messed up, a dish for Alma Lach, also a Cordon Bleu cook. Lach and her husband Donald, a history professor at the University of Chicago, are resident masters of a student dorm. Every Sunday night the Lachs treat about 60 students to an elaborate dinner. One of the receipes she wanted to make was a seafood souffle, but she had trouble with the timing for such a large quantity.

"I found I couldn't do a real souffle because the timing was just too exact. So instead I decided to make a phoney souffle, using the same technique you use in making bread pudding. I buttered and cubed bread, added sauteed onions and mushrooms, then a mixture of eggs, milk and cream seasoned with dry mustard and basil. When you bake it, the flour in the bread causes it to inflate and the dish puffs up just like a souffle -- yet you put everything together the day before."

Lach, who currently teaches French and Chinese cooking, thinks some of her best creations are made by cooking in one cuisine and borrowing from another. She makes duck a l'orange with julienne strips of fresh ginger, which she first simmers in a mixture of sugar, water, a little orange juice and orange liqueur.

Lach, like Reis, sometimes gets ideas from other chefs, though trying to duplicate a taste without a recipe is often more difficult than creating a whole new dish. When Lach and her husband lived in Paris, she coveted the Grand Marnir souffle at Laperouse, but the chef was mum. She made the souffle for dinner six night a week for a month in an attempt to create an exact copy. On the seventh night, the Lachs would go to the restaurant to see how close she had come.

Fifteen dozen eggs later she cracked the laperouse souffle, then had to start over again back in the States because the flour is different here.

Lach, as well as Reis and Spitler, all believe Amerian cooks should experiment more. Spitler, in particular, enphasizes trying out unfamiliar herbs. first in a vinaigrette, where the flavor stand out.

"Make just a little, and try it on a few lettuce leaves."

Reis advises making notes beside recipes and improvising from there. (Her own tattered "Joy of Cooking" is filled with remarks in the margins -- "too much tarragon," "not enough mushrooms." "add some tomato paste."

Lach suggests getting comfortable with a few basics, then trying variations ("In all of French cooking there are only about 30 or 40 basic recipes; the rest are variations").

"The problem for most cooks," said Lach, "is that they're afraid of lousing something up. But the only thing you can really louse up is a cake. The proportions have to be exact or the thing won't rise properly."

Spitler is a little more realistic.

"Sometimes when I'm doing a new dish, I put it in the oven, cross my fingers, and pray." SUE SPITLER'S EASIEST PUFF PASTRY 21/2 cups all-purpose flour 1/2 teaspoon salt 3/4 pound frozen butter cut into pieces 1/3 cup plain yogurt or sour cream 1 egg

Insert steel chopping blade in food processor. Process flour, salt and butter until mixture forms coarse crumbs. Add yogurt and egg. Process until dough almost forms a ball. (Dough will be somewhat sticky.)

Form dough into rectangle on well-floured surface. Roll into rectangle, 24-by-8 inches. (Dough will be about 1/4-inch thick.) Fold short ends in to meet at center; fold in half like a book. Turn dough so that short end is facing you; repeat rolling and folding instructions. Wrap dough in plastic wrap. Refrigerate 4 hours or overnight. Use in desired recipes.

Note: Pastry can be frozen up to 6 months. Thaw in refrigerator. SUE SPITLER'S STRAWBERRY PASTRIES (2 dozen) 1 recipe Easiest Puff Pastry 1/2 cup strawberry or other fruit preserves

Roll pastry on floured surface to 1/4-inch thickness; cut into 3-inch squares. Spoon teaspoon preserves into center of each square; fold corners of pastry to center and pinch to seal. Place on ungreased cookie sheet. Bake at 400 degrees for 15 minutes or until golden. Serve warm. Puff pastry recipe developed for Southern Living's cooking school. LESLEE REIS' CAULIFLOWER MOUSSE WITH TOMATO SAUCE (6 servings) 2 pounds head cauliflower 2 eggs 1/2 cup heavy cream, scalded Salt White pepper Freshly grated nutmeg

Wash and trim cauliflower head. Cut out core; discard. Cut head into flowerets, and cook in large pot of salted boiling water, uncovered, about 6 minutes, or until tender. Drain. Puree in food processor or blender. Add eggs and cream and blend. Season to taste with salt, pepper and nutmeg.

Butter insides of 6 individual timbales. Cut parchment for bottoms, butter and place in timbales. Fill, set in hot water bath, and bake at 350 degrees about 40 minutes or until just firm to touch. Let sit at least 10 minutes (and up to 20) to firm up. Unmold and serve with fresh tomato sauce. Fresh Tomato Sauce 4 or 5 ripe tomatoes 3 tablespoons peanut oil 3/4 tablespoon sherry wine vinegar Salt Freshly ground pepper

Peel and seed tomatoes, saving the juice, then dice them. Place pieces in a saucepan, add juice, peanut oil, vinegar and salt and pepper to taste. Warm for about 5 minutes. Serve with cauliflower mousse.

Note: If fresh tomatoes are not red-ripe, use a few for texture, but for taste and color, add canned Italian plum tomatoes. ALMA LACH'S OVERNIGHT SOUFFLE (8 servings) 10 slices sandwich bread (soft king) 3/4 cup butter, softened, plus 1/2 cup butter 1 teaspoon basil 1/2 teaspoon salt 1 teaspoon seasoned salt 1 teaspoon sugar Freshly ground pepper 1/2 teaspoon dry mustard 1 teaspoon Worcestershire sauce 2 cups milk 6 large eggs 2 large onions, diced 1/2 pound mushrooms, sliced Salt, pepper and sugar to taste Seafood sauce 8 raw, cleaned jumbo shrimp (about 2/3 pound) 1/2 pound sea scallops 1/2 cup butter, unsalted 4 shallots, minced 1 clove garlic, minced 6 tablespoons flour 1/2 teaspoon salt 1 teaspoon sugar 1 1/2 cups milk 1 cup whipping cream 1/4 cup Madeira or sherry 1 tablespoon lemon juice Minced parsley

Butter bread slices liberally with 3/4 cup softened butter.Cut into 1/2-inch cubes; put in large (3 to 4 quart) casserole.

Combine basil, salts, sugar, pepper, mustard and Worcestershire in a bowl. Add enough milk to make a paste. Add eggs; blend well. Add remaining milk. Pour over bread cubes and mix. Cover and refrigerate overnight.

When ready to bake souffle, saute onions in 1/2 cup butter for about 5 minutes. Add mushrooms and saute for about 5 minutes. Season to taste. Stir into bread mixture. Bake 1 hour at 350 degrees or until puffed and brown. Do not cover.

While souffle bakes, prepare seafood sauce: cut shrimp into 1/2-inch pieces. Slice each scallop horizontally into 2 or 3 slices; wash in cold water. In skillet, saute seafood in 1/2 cup butter for about 2 minutes. Remove to a plate.

Add shallots and garlic to skillet and cook until liquids are reduced and only butter remains in pan. Add flour and cook, stirring, 3 minutes. Add salt, pepper, sugar, milk and cream. Cook, stirring, until thick.

Drain juice off seafood into sauce. Add Madeira and lemon juice. Taste and adjust seasonings. Add seafood and heat just to warm through. Spoon sauce over souffle and sprinkle with parsley.