Powdered buttermilk is strictly for baking or seasoning. Mix the powder with other dry ingredients or reconstitute it. Dry, reconstituted buttermilk or buttermilk from the dairy case can be used for baking desserts, such as mini triple-chocolate buttermilk pound cakes, buttermilk-pecan pralines, buttermilk pie, or lemon-buttermilk icebox pie. Powdered buttermilk, when stored properly, can last for years.