Less-than-fresh baking powder can be the difference between the Ultimate Chocolate Chip Cookies and hockey pucks. Baking powder is a leavener—it produces carbon dioxide bubbles that help dough rise and make for tender baked goods. Here's how to make sure the stuff in your pantry is still fresh enough to do the job.
If it falls flat, try making your own! For the equivalent of 1 teaspoon of baking powder, combine 1/8 teaspoon cream of tartar with 1/4 teaspoon baking soda.