Eggs. Purchase clean, fresh eggs from refrigerated display cases. At home, refrigerate them promptly in their original carton. Do not wash eggs before storing or using them, and discard eggs with cracked shells. Use raw eggs within one week of purchase, although they can be refrigerated safely for as long as five weeks.
Fats. Butter produces the richest, tenderest, and most flavorful cookies. Salted and unsalted butter can be used interchangeably; however, if you use unsalted butter, you'll need to increase the amount of salt in the recipe (1/4-teaspoon salt per 1/2-cup unsalted butter). Store butter in the refrigerator for up to one month or in the freezer for six to nine months. Shortening is a solid fat that has been made from vegetable oil. It now comes packaged in sticks conveniently marked with tablespoon and cup measurements. Shortening can be stored at room temperature for up to a year. Plain and butter-flavored types are available; use whichever you prefer for baked products. If an icing recipes calls for shortening and you want the icing to be white, use plain shortening for a cleaner color.
Sugars. When a recipe calls for sugar, use white granulated sugar. Powdered sugar or confectioners' sugar refers to granulated sugar that has been pulverized; cornstarch is often added to prevent clumping. Sift powdered sugar before measuring. Brown sugar is a mix of granulated sugar and molasses; the amount of molasses determines whether the sugar is light or dark. If you purchase sugar in boxes, transfer it to a sealed plastic bag or an airtight container. When stored in a cool, dry place, sugars will keep indefinitely.
Flours. Store all-purpose and whole wheat flour in sealed plastic bags, or transfer them to airtight storage containers and keep them in a cool, dry place. All-purpose flour will stay fresh 10 to 15 months; whole wheat flour will stay fresh up to 5 months.
Leavenings. Both baking powder and baking soda are important to baking, making cookies rise and become light. Store them in airtight containers in a cool, dry place. For best results, check the expiration date on the packages or replace them every 6 months.