Our recipes mostly include butter, sugar, eggs, flour, and leavening. Be sure to use real butter, not margarine (which contains some water and will alter the texture). Some recipes call for various types of sugar―powdered sugar to dissolve easily, granulated sugar to create bulk and crunch, or brown sugar to contribute moisture and caramel-like flavor. Eggs usually provide the only liquid in the dough, and almost all of the recipes use all-purpose flour. Some call for baking powder, baking soda, or both.
A hand or stand mixer is used for most of our recipes; either one easily combines ingredients and whips in air for a lighter texture. Bake on heavy, shiny metal baking sheets (flat pans, which may have a lip on one or both ends); cookies baked on nonstick sheets tend to brown too much on the bottom. We don't advise baking on rimmed jelly-roll pans because the rims may deflect heat. Lining pans with parchment paper prevents sticking, and you can reuse the paper for each batch. For bar cookies, bake in shiny metal pans, not glass baking dishes; glass conducts heat differently and may cook the cookies too quickly. Cooling racks allow air to circulate under the cookies as they cool so they won't become soggy.
As with all baked goods, measure ingredients with precision, and use the exact ingredients specified. Many of the recipes first cream together butter and sugar, then add the dry ingredients. For these recipes, start with softened butter―butter that yields slightly to pressure but doesn't lose its shape when touched. It's important not to overmix the dough once the dry ingredients are added, as doing so may result in tough cookies or ones that don't rise well; mix just until the ingredients are combined. Many of the doughs are chilled before baking; this solidifies the fat and helps prevent overspreading as the cookies bake.
Be sure your oven is preheated; you might want to use an oven thermometer for accuracy. Always place dough on cool baking sheets because warm or hot pans will cause the cookies to spread or puff too much. You can quickly cool a baking sheet by placing it under cold running water; dry thoroughly before arranging dough on the pan. Allow room for spreading so cookies don't bake together. In general, bake cookies on the second rack from the bottom. If you bake two pans at once, rotate them halfway through the cooking time. Allow baked cookies to stay on the pan for a few minutes before transferring them to cooling racks; trying to move them too soon can result in broken cookies.