Eggs are a critical leavening agent for cream puffs, making the batter rise and expand. Piercing the cooked puffs allows steam to escape so the texture is almost hollow. A stand mixer is crucial; the batter is too thick to beat with a hand mixer. Freeze completely cooled cream puffs for up to one month. Cream puffs are also good with savory fillings, such as chicken or shrimp salad.