The term 'Hollow Pastry' refers to two types of pastries: Puff (4 letters) and Popover (7 letters). Puff is a light, airy pastry made from flour, butter, eggs, and milk. It is usually baked in a hot oven until it is golden brown and puffy. Popover is a similar pastry, but it is made with a batter that is poured into a hot pan and then baked until it is golden brown and hollow. Both pastries are often served with sweet or savory fillings.