Choux (pronounced "shoo") are puff shells made from a thick batter (pate a choux) of butter, flour, eggs, milk and water. The mixture is cooked on the stovetop, then fashioned into a variety of shapes and sizes and slipped into a hot oven to bake. The moist interior and crisp shells are ideal for savory or sweet fillings. Small puffs are often used to make profiteroles. Store the shells in an airtight container at room temperature for up to 1 day, or make them ahead and freeze for up to 1 month.