only when butter is used.
1. Use the right fat. Recipes calling for butter or margarine will produce good results with either, as long as you use a margarine that contains at least 80 percent vegetable oil. If it's not clear from the front of the box, check the nutrition label: The margarine should have 100 calories per tablespoon. Margarines with less than 80 percent vegetable oil have a high water content and can result in tough cookies that spread excessively, stick to the pan, or don't brown well.
2. Measure accurately. Nested metal or plastic measuring cups are intended for dry ingredients such as flour and sugar. When you measure flour, stir it in the canister to lighten it (you don't need to sift). Gently spoon flour into a dry measuring cup and level the top with the straight edge of a metal spatula or knife. Don't pack the flour into the cup or tap it with the spatula or on the counter to level. Glass or plastic cups with a spout are meant only for liquids. If you use a liquid-measuring cup for flour, you're likely to get an extra tablespoon or more of flour per cup, enough to make cookies dry.
3. Chill dough properly. The chilling time given in a recipe is the optimum time for easy rolling and shaping. If you need to speed up the chilling, wrap the dough and place it in the freezer. About 20 minutes of chilling in the freezer is equal to one hour in the refrigerator. Always chill rolled or sliced cookies made with margarine in the freezer.
4. Choose the right cookie sheets. Look for shiny, heavy-gauge cookie sheets with very low or no sides. Avoid dark cookie sheets, which may cause cookie bottoms to overbrown. Use jelly-roll pans (15 x 10 x 1-inch baking pans) only for bar cookies. Other types of cookies won't bake evenly in a pan with an edge. If you must use such a pan for cookies, turn it over and bake on the bottom. Nonstick cookie sheets let you skip the greasing step. However, the dough may not spread as much, resulting in thicker, less crisp cookies.