EVEN AN experienced cook may agonize over the purchase of the butter, worry about the oven temperature and the proper measuring of the flour, feel intimidated by the rolling pin. But at some point the next step is so easy, so obvious, that every cook -- experienced or beginning -- feels on firm ground.

Stir, says the recipe.

That's a cinch, the cook responds.

Not so fast, I say.

You can find just as many fine points, pitfalls, violent differences of opinion in stirring as in serving wine. As with everything else, there are stirring snobs.

Stirring, at the most basic level, is blending. And its boundaries are carefully protected. If you try to incorporate air as you blend, you have slipped over into beating. And if you try to preserve the air already in the mixture, you are probably in the territory of folding.

Leaving aside beating and folding, if you care about the fine points, stirring alone can burden you with enough rules to turn you into an obsessive bore -- and disgustingly perfect in your cooking products. You could, for example, take the trouble to learn when to stir and when not to stir. You could develop an understanding not only of the proper speed at which to stir any particular dish, but also the rate of stirring (as you add ingredients slowly or quickly). You delve into the optimal utensils, the proper temperature, the hand-and-wrist technique, and even the geometry of stirring.

This, then, is the pedant's guide to stirring.

Some things, of course, should never be stirred. Modern martinis, their drier gin and minimal vermouth making a more raw drink than was common in the old days, should be shaken with ice, to chill them quickly without diluting them and to avoid, some say, bruising the poor drink. At the other end of some spectrum, fudge -- once the sugar mixture has reached 130 degrees -- must be cooked without stirring or even jostling, through the stirring must be resumed when it has cooled down to 110 degrees, and continued until the fudge loses its sheen. You must also take care not to stir -- at all -- the syrup for glazed fruit while you are dipping the fruit.

Less critical, but worth considering, is shaking, rather than stirring beans while they are cooking. The concern in this instance is not over a chemical reaction, but the fragility of the beans. And one of the finest points in all stirring lore suggests that, in adding the finishing touch to a sauce, a dollop of butter to give it sheen, it should be swirled rather than stirred. "The Joy of Cooking" is quite firm on the point, instructing the cook to move the pan in a circular motion so that the butter makes an actual swirl in the sauce melts, but definitely not to use a spoon to stir it. Madaleine Kamman, in "The Making of a Cook," limits her swirling to deglazed custard sauces, where the eggs and cream are shaken back and forth in the pan until they coat the food. Julia Child equivocates. She instructs to beat butter into sauces, switching to swirling for sauce diable.

Timing is crucial, especially with cooked sugar and chocolate.Sugar and water must be stirred constantly, but just until it boils; after that, stirring will crystalize the sugar. Chocolate, likewise. Furthermore, the spoon to stir it must be absolutely dry; one drop of water will coagulate the melted chocolate.

Some foods are stirred just a little: muffin batter is stirred just to moisten, as is pie dough. Otherwise, the gluten in the flour will toughen the final product. Lemon pie filling with thin if it is stirred too much during cooking. Salad dressings, mayonnaise and hot butter sauces such as hollandaise, on the other hand, require such thorough stirring that the oil or butter must be very gradually added while the stirring continues.

Possibly the most complex stirring instructions in print are Kamman's for pate a choux, cream puff shells: "dry the paste, i.e., keep it contantly in movement on the bottom of the pan so that as much as possible of its volume is exposed to the heat. Hold the pan handle with the left hand, a wooden spatula in the right hand. In three strokes, flatten the paste on the bottom of the pan, bringing it against the side of the pan closest to you. With one flip of the spatula, throw the bulk of the paste back to the opposite side of the pan."

Then there is the geometry of stirring. Fanny Farmer teaches that stirring should be circular, widening the circle until the entire mixture is blended. Some dishes, such as the lamb and yogurt below, for example, must be stirred in one direction only. Others -- for example, cheese sauces -- must never be stirred in only one direction; the cheese will become ropey.And finally, there are the delicate preparations such as custards, which "The Good Cook/Classic Desserts" by Time-Life Books, explains must be stirred in a figure 8, "so that you pass the spoon through the middle -- the hotest part -- twice in each complete motion."

Which brings us to utensils. That same custard should be stirred with a square-edged spoon which will reach the corners of the pan. Wooden spoons are most frequently preferred, especially for heating, since they don't conduct heat to your hand. Probably the oldest utensils in the world (developed from flattened sticks), wooden spoons are also cheap and comfortable to hold. And they float if dropped into the soup. Sometimes, however, cooking requires more than one spoon; if you are making caramel or nougatine and the sugar sticks to the spoon, French confectionery expert Gaston Lenotre cautions you to use another spoon rather than scrape it off. Sometimes you use two spoons simultaneously, as in Roger Verge's sauteed spinach (from "Cuisien of the South of France"). And often you don't use a spoon at all; stirring pie dough with a fork keeps it from being overworked or overheated. But it takes two forks for stirring sauces into pasta. Then, sometimes you use common sense; as Sandra Oddo cautions in "Homemade," you strew oatmeal by into boiling water for porridge, "stirring the mixture all the time with the other hand (which holds a spoon)."

There is often the question of what gets stirred into what. With eggs and hot liquids, the answer is that the hot liquid gets stirred (gradually) into the eggs. Unless you are making egg drop soup.

If you're a cook looking for a fight, you bring up the subject of mashed potatoes or omelets. Kamman is adamant: potatoes must be pushed through a food mill with only downward motion, no back-and-forth stirring sort of motion, or they will become gummy. One hot cream is added, you beat them. Roger Verge is no less stern; when you blend in the butter, you must stir (with a wooden spoon, certainly) constantly, with absolutely no stopping, until the potatoes are glossy.

Omelets are worse. Culinary world wars are threatened over whether the omelet should be stirred constantly (the English favor that) or occasionally, lifted and folded or shaken, or stirred and shaken at the same time, much like patting your head and rubbing your tummy simultaneously. Julia Child lists two alternative methods, Roger Verge four, Madeleine Kamman three, one of them a shake-and-throw method hardly less complicated than her cream puff instructions.

But none matches the degree of commitment required by the recipe once printed in a food magazine that shall be allowed to rest in peace: "Refrigerate overnight, stirring occasionally." BARBARA ALEDORTS LAMB IN YOGURT (4 to 6 servings) 2 pounds boned leg of lamb, cut into 1-inch pieces 1 cup onions, chopped 1/2 cup water 1 teaspoon salt 1/4 teaspoon allspice 1/4 teaspoon cinamon 1/4 teaspoon freshly ground white pepper 1 tablespoon cornstarch 1 egg 1 1/2 cups unflavored yogurt Taklia: 1 tablespoon butter 2 cloves garlic, crushed to a paste with a little salt 1 tablespoon fresh mint, chopped, or 1 1/2 teaspoon dried

Place the lamb and the onion in a heavy casserole. Add water, salt, allspice, cinnamon and freshly ground pepper. Cook, covered, for about 1 hour or until the meat is very tender.

In a saucepan, whisk the cornstarch and the egg into a little yogurt, beating until smooth with a wooden spoon. Stir in the remaining yogurt. Bring to the boil slowly, stirring constantly in one direction only. Lower the heat and continue to cook, stirring, until the yogurt is thick and creamy, about 10 minutes. Fold in the meat, onion and cooking juices. Continue to cook for a few minutes to blend flavors.

To make the taklia, heat 1 tablespoon butter in a skillet and saute the garlic and mint for 1 minute. Stir into the lamb mixture. Readjust the seasoning and serve hot with rice pilaf.

Note: If recipe is doubled, do not use all cooking juices, as they will thin the sauce too much. Adapted from Paula Wolfert's "Mediterrannean Cooking" FUDGE COCKAIGNE (Makes 1 1/4 pounds) 1 cup, minus 1 tablespoon, rich milk 2 cups sugar 1/8 teaspoon salt 2 ounces baking chocolate, grated 2 to 4 tablespoons butter 1 teaspoon vanilla 1/2 to 1 cup broken nut meats

Bring milk to a boil in a large heavy pan. Remove from heat and stir in sugar, salt and chocolate, continuing to stir until dissolved. Bring to a boil and cook covered 2 to 3 minutes until the steam washed down from the sides of the pan removes any crystals which may have formed. Uncover, reduce heat and cook without stirring to a soft-ball stage, 238 degrees. When nearing 238 degrees, there is a fine overall bubbling with, simultaneously, a coarser pattern, as though the fine bubbled areas were being pulled down for quilting into the coarser ones. Remove from heat and cool candy to 110 degrees. You may hasten this process by placing the hot pan in a larger pan of cold water until the bottom of the pan has cooled.

Add butter, beat partially. Add vanilla and beat until it begins to lose its sheen. At this point the drip from the spoon, when you flip it over, holds its shape against the bottom of the spoon. Quickly add nut meats.

Pour the fudge into a buttered pan. Cut into square before it hardens. To use fudge for centers, beat until thick, knead and shape. From "The Joy of Cooking" POTATO PUREE OR MASHED POTATOES (6 servings) 6 medium Idaho or Maine potatoes Salt 1/3 cup heavy creams, scalded 3/4 cup butter Grated nutmeg (optional)

Peel potatoes, cut into pieces, and cover with cold water. Bring to a boil and add 1 teaspoon salt per quart of water. Simmer for 18 to 20 minutes; drain. Push the potatoes through a tamis or conical strainer. Add the scalded heavy cream and the butter. Beat well with a wooden spoon or spatula to homogenize. Correct the seasoning and add nutmeg if desired. Serve with any meats. From Madeleine Kamman's "The Making of a Cook" BASIC POURING CUSTARD %[Makes 2 1/2 cups] 6 egg yolks 1/4 to 1/2 cup superfine sugar 2 1/2 cups milk, scalded and slightly cooled

In a mixing bowl beat the eggs and sugar together with a wire whisk until the mixture is thick and pale, and forms a slowly dissolving ribbon when dribbled from the whisk. Whisking gently all the time, slowly add the scalded milk.

Transfer this custard mixture to a heavy saucepan. Put the saucepan over low heat. Taking care to keep the custard below the simmering point (do not let it boil), stir it in a figure 8 motion so that you pass the spoon through the middle -- the hottest part -- twice in each complete motion. A square-edged spoon will reach into the corners of the pan where the sides join the bottom and thus will prevent patchy thickening. The consistency is correct when the custard coats the spoon. At this point, immediately dip into a bowl of ice mixed with a little water to stop mixture from cooking further and possibly curdling. To insure a smooth texture, continue to stir the custard for 5 minutes until it cools a little. To remove any lumps, strain the custard into a bowl.

For a warm custard, set the bowl in a pan partly filled with hot water and stir the custard occasionally. For a cold custard, set the bowl over ice cubes until the custard is sufficiently chilled. From Time-Life Books' "Classic Desserts" The Three Methods of Making an Omelet

Scrambled Omelet: This method is mostly used in England and the United States. With the left hand, shake the pan back and forth on the burner while the right hand stirs the eggs in a circular motion. Work with lightning speed (my French friends and I call this omelet the "agitation" omelet) and try not to scrape the bottom of the pan. Within 15 seconds, the eggs are scrambled. Tilt the pan at a 45-degree angle, bunch the eggs at the lower end of the pan, and invert them on a plate.

Beaten Omelte: This is the French home method, and is also taught at the Cordon Bleu in Paris. Pour the omelet mixture into the pan. Let it set for 5 seconds, counting 1 when the mixture hits the pan. Then beat with a folk, introducing as much air as possible into the eggs until they are scrambled. Shake the pan back and forth 3 times to make sure the omelet slides easily in the pan. Let it slide forward almost out of the pan. With a spatula, fold the flap hanging out of the pan back upon itself; slide the spatula under the portion of egg still on the bottom of the pan and fold it over the first flap. Invert on a plate.

Shaken Omelet: Pour the omelet mixture into the pan; let it set for 8 seconds, counting 1 when the mixture hits the pan. Grab the handle of the pan with both hands and raise the pan so it forms a 45-degree angle with the burner. Shake the pan back and forth so that the egg mixture is thrown against the front lip of the pan and coagulates there. Very soon the batter forms a dam enclosing still-liquid egg; quickly give a circular motion to the pan to let the liquid portion pour out into the pan. Continue both shaking and circular motions until the eggs are scrambled; the whole operation requires 15 seconds. The lower portion of the omelet will fold upon itself, forming the first flap. Raise the pan a litter higher and fold the second flap over the first with a spatula; or do it by hitting the pan handle with the right fist. Invert the omelet on a serving plate. From Madeleline Kamman's "The Making of a Cook"