1. Work with half of the cookie dough at a time when rolling and cutting cookies. Too much handling of the dough makes cookies tough.
Keep the other half refrigerated. Chilled dough is easier to handle.
2. Bake cookies on shiny, heavy aluminum baking sheets. These sheets with no sides are designed for easily sliding cookies onto a cooling rack. Dark sheets may absorb heat, causing cookies to brown too much on the bottom; nonstick baking sheets work well if not too dark. Insulated baking sheets require a slightly longer baking time.
3. Grease baking sheets with cooking spray or solid shortening instead of butter or margarine. Avoid using tub butter or margarine products labeled as spread, reduced calorie, liquid, or soft-style. These contain less fat than regular butter or margarine and do not give satisfactory results.
4. Use parchment paper to eliminate the need for greasing baking sheets. It also promotes even browning.
5. Bake 1 sheet of cookies at a time on the middle oven rack; if you need to bake more than one at a time, rotate the sheets from the top rack to the bottom rack halfway through baking to encourage even browning.
6. To make brownies and bar cookies, line a baking pan with heavy-duty aluminum foil; allow several inches to extend over the sides. Lightly grease the foil. Spread the batter evenly in the pan; bake and cool. Lift from the pan, using edges of the foil. Press down the foil sides; cut cookies into the desired size and shape with a dough scraper (available at kitchen-supply stores).
7. Check cookies for doneness at the minimum baking time.
8. Cool baking sheets between batches before reusing; wipe the surface of each with a paper towel.
9. Place a sheet of wax paper on the counter and sprinkle it with sugar if you're short on cooling racks. Cookies will cool without getting soggy.
10. Cool cookies completely before storing them in airtight containers.