WITH PRICES as high as they are, most people find it more painful than ever to throw away food, especially something nourishing. So, it is particularly frustrating when a recipe results in leftover egg yolks or whites. If you know how to store them, however, you can turn them from waste into "finds" and put them to good use.

The size of the egg can greatly affect a recipe. Egg size is determined in this country by the total weight of a dozen eggs. A dozen "medium" eggs weigh 21 ounces, "large" weigh 24 ounces, and "extra-large" weigh 27 ounces.

In this regard, the yolks and whites in most recipes mean those from large eggs. A typical large-size yolk measures about 1 1/3 tablespoons in volume, while a large-size white is about 2 tablespoons.

Occasionaly, a particular cookbook author will choose another size. For example, Maida Heatter uses "extra-large" eggs and Gaston Lenotre prefers "medium." (This fact should be stated in the introduction to a cookbook.)

Eggs are easiest to separate when they are cold because the yolk is less likely to break. But, as most cooks know, whites will beat to a higher volume if they are at room temperature. Since shelled eggs are highly perishable, they should not be allowed to stay at room temperature for too long.

Eggs can be separated in a number of ways. One of the most classic is to evenly break the shell, then pass the yolk back and forth between the two halves as the white drops off.

There are several gadgets available that do the same thing. But the cheapest and easiest, though messiest, method is to break the egg into the curved palm of one hand. When the fingers are spread slightly apart, the white falls through while the yolk stays gently cradled in the hand. This is a great method for children to use. They just love the slippery feeling, and it is more reliable than using the shells.

Extra yolks and whites can be stored in the refrigerator for one or two days. Intact yolks should be covered with a layer of cold water that is poured off before they are used. Whites keep best in small, airtight plastic containers.

Actually, the very best place to store whites is in the freezer. Once thawed, they can be used exactly like fresh whites, and some experts even say they beat higher. To freeze whites, simply place each one in the individual well of a plastic ice cube tray and cover with plastic wrap. When frozen, pop out cubes and store in a freezer bag or plastic container. One cube equals one fresh white.

Or, freeze any number of whites in an airtight plastic container or glass jar, making sure to leave some headroom for expansion. Label the front with the amount. You can add more whites to this container as they become left over, until you have the number needed for a special recipe.

Yolks can also be frozen, although the results are not as good as with whites. The yolks need to be stabilized with sugar (or honey or corn syrup) or salt -- the choice depending on how you will eventually use them -- or they will become pasty and hard to mix. Stir either 3/8 teaspoon sugar (or the same amount of honey or corn syrup) or 1/8 teaspoon salt into every 3 yolks before freezing. (That's equivalent to 1 1/2 teaspoons sugar or 1/2 teaspoon salt per cup of yolks.) Label each container accordingly. Yolks or whites frozen in a vapor-proof, moisture-proof container will keep about a year.

Thaw frozen yolks or whites overnight in the refrigerator. If you are in a hurry, a cold-water bath can rush things along. Small quantities can even be left at room temperature to thaw, if you don't let them stay warm too long.Use yolks or whites as soon as possible after thawing, perhaps in the following recipes: LEMON CURD (Makes 1 to 1 1/4 cups)

This is a popular English custard-butter used as a spread for toast, a filling for cakes, cookies or small tarts, or as a topping for gingerbread. The flexible recipe is quick to prepare, and can be frozen quite successfully. It can also be stored in the refrigerator for a week or so. 4 to 6 "large" egg yolks 1/4 cup lemon juice (preferably fresh) 1/4 cup butter, cut into small pieces 1/4 to 1/2 cup sugar or very mild honey 1 to 2 teaspoons lemon peel

Place all ingredients except lemon peel in a medium saucepan. (Start out with smaller amount of sugar of honey, and add more to taste later, if desired.)

Cook over medium heat, stirring constantly, until butter is melted and the custard is thick enough to coat a spoon. (Do not let it get too hot or it will curdle. You can use a double boiler to help prevent this from happening. If it does, you may be able to save the lemon curd by immediately whizzing it in a food processor.)

Remove lemon curd from heat, and stir in additional sugar or honey, if desired, and lemon peel. Continue stirring until lemon curd is slightly cooled and extra sugar is dissolved. store in refrigerator or freezer, and serve chilled. Lemon curd will thicken considerably as it cools. ZABAGLIONE (4 to 5 servings)

This elegant, frothy Italian dessert (pronounced zah-bah-yoh-nee ) is classically served warm, as soon as it's made, with some dainty cookies.It's also very good chilled.

The recipe can be infinitely varied by substituting various wines for the marsala, or by using rum or liqueur. The amounts of liquid and sugar should be altered to taste. By the way, the French call this sort of dessert sabayon, and often use it as a sauce over fresh fruit. 6 "large" egg yolks 6 tablespoons sugar (or less, if wine is very sweet) 1/2 to 3/4 cup marsala wine, to taste

Place the egg yolks and sugar in the top of a double boiler. Beat with a wire whisk until light and fluffy, then beat in the wine. Place over simmering water, and continue to rapidly beat with the whisk as the mixture is warmed. Beat continually until the mixture foams and thickens enough to briefly retain a slight peak. Do not let the zabaglione get too hot or it may curdle.

Serve in stemmed wine glasses or dessert cups. Accompany with fancy cookies such as pirouettes or tuiles, or with fresh fruit such as strawberries. EASY BLENDER HOLLANDAISE SAUCE (About 3/4 cup) 3 "large" egg yolks 2 tablespoons lemon juice, preferably fresh Pinch salt Pinch freshly ground white pepper 1/2 to 2/3 cup butter, melted and bubbling hot

Place yolks, lemon juice, salt and pepper in blender jar. Cover and blend for about 30 seconds. Uncover top, removing only the center of it, if possible. With blender running (on a medium speed), slowly dribble in 1/2 cup of the hot, melted butter. Continue blending about 1 minute longer until sauce is thick and creamy.

Remove sauce from blender jar and taste. If it is too lemony or you desire more butter, beat in by hand an additional tablespoon or 2 of hot, melted butter.

Serve warm sauce over cooked, fresh green vegetables such as asparagus, broccoli, string beans or artichokes.

(Note: This sauce can be made in advance and stored in the refrigerator. To warm again, heat in a double boiler over simmering water, constantly stirring, until sauce is warmed through. Do not overheat, or sauce will curdle.) SWISS BROYAGE MERINGUE (2 8-inch rounds)

This is a fancy sort of meringue that includes nuts as a basic ingredient. It can be made into any shape, and used as a delightfully crunchy layer between layers of cake. Or it makes a nice dessert on its own -- especially when topped with fruit or buttercream icing. 3 "large" egg whites 1/8 teaspoon cream of tartar Pinch of salt 1 teaspoon vanilla extract 2/3 cup sugar 1/4 cup finely grated almonds (or other nuts) 1/3 cup sifted cornstarch 1/4 teaspoon almond extract (optional)

Place egg whites, cream of tartar, salt and vanilla extract in a large, clean mixing bowl. Beat on medium speed until egg whites hold soft peaks. Gradually add about half of the sugar, and continue beating at high speed until the meringue is very shiny and stiff. Fold in the remaining sugar, finely grated nuts, cornstarch and, if desired, almond extract.

Trace 2 8-inch circles (or any shapes to cover an equivalent area) on baking parchment, waxed freezer paper or waxed paper, and place paper on a baking sheet. Fill in outlines with the meringue (so that it is about 1/4 inch thick), and use spatula to smooth tops. (A pastry bag makes it very easy to neatly distribute the meringue.)

Bake in a preheated 325-degree oven for 35 to 40 minutes, or until broyage is very lightly browned and firm. Carefully peel off paper, and cool completely before using or storing. Swiss broyage keeps very well in an airtight container. CHICKEN WITH FRESH BEAN SPROUTS (4 servings) 4 chicken breast halves, boned and skinned 1 1/2 tablespoons cornstarch 2 "large" egg whites, lightly beaten 1 1/2 teaspoons salt 1 1/2 tablespoons dry sherry 4 tablespoons peanut oil 4 cups fresh bean sprouts 1 scallion, thinly sliced on the diagonal

Cut chicken breasts into very thin slices about 1 1/2 to 2 inches long. (This is easiest to do when chicken is slightly frozen.) Place chicken slices in a bowl, and toss with cornstarch. Add egg whites, 1 teaspoon of the salt, and the dry sherry. Mix thoroughly. Let chicken marinate while preparing bean sprouts.

Heat 1 tablespoon of the oil in a large skillet or Chinese-style wok over high heat. Add bean sprouts and scallion, and sprinkle with the remaining 1/2 teaspoon salt. Stir-fry -- that is, lightly toss while continuously stirring -- about 2 minutes, or until sprouts are heated through but still crunchy. Remove sprouts with a slotted spoon; then clean out pan with paper towel.

Heat the remaining 3 tablespoons oil in the pan. Give the marinating chicken pieces a quick stir; then add to the pan. Rapidly stir-fry until chicken turns completely white and is cooked through (it should only take a few minutes). Add the bean sprouts back to the pan, and stir-fry with the chicken about 30 more seconds. Serve immediately.