Any fluffy baked good needs two components: architecture, the thing that gives it shape and structure, and a leavening agent, to make it rise. In this recipe, the architecture comes from gluten in the flour and rise from baking powder. (Author's note: If you've ever wondered about the difference between baking powder and baking soda, think of the classic elementary-school volcano experiment, in which baking soda combines with acidic vinegar to form water and bubbles of carbon dioxide. Baking powder contains both baking soda and an acid, as well as corn starch to stabilize the components. When exposed to heat, the powder's ingredients react, creating bubbles.) The trick to a perfectly cooked cake (in the microwave or in the oven) is making sure your architecture sets at the same time that your leavening agent—in our case, baking powder—forms air bubbles to make the batter rise.