Quevedo caustically suggests that the puff pastry pies sold at the inn of some Simón de Paredes in Madrid were being adulterated with human flesh. Production The production of puff pastry dough can be time-consuming, because it must be kept at a temperature of approximately 16 °C (60 °F) to keep shortening from becoming runny, and must rest in between folds to allow gluten strands time to link up and thus retain layering. The number of layers in puff pastry is calculated with the formula: where is the number of finished layers, the number of folds in a single folding move, and is how many times the folding move is repeated. For example, twice-folding (i.e. in three), repeated four times gives layers. Chef Julia Child recommends 73 layers for regular pâte feuilletée and 729 (i.e. 36) layers for pâte feuilletée fine (in Volume II of her Mastering the Art of French Cooking textbook). Commercially made puff pastry is available in grocery stores. Common types of fat used include butter, vegetable shortenings, lard and margarine. Butter is the most common type used because it provides a richer taste and superior mouthfeel. Shortenings and lard have a higher melting point therefore puff pastry made with either will rise more than pastry made with butter, if made correctly. Puff pastry made in this manner will, however, often have a waxy mouthfeel and more bland flavor. Specialized margarine formulated for high plasticity (the ability to spread very thin without breaking apart) is used for industrial production of puff pastry. Variants and distinctions Since the process of making puff pastry is generally laborious and time-intensive, faster recipes are fairly common: known as "blitz", "rough puff", or "flaky pastry". Many of these recipes combine the butter into the rather than adding it in the folding process and are thus similar to a folded short crust. Puff pastry can also be leavened with baker's yeast to create croissants, Danish pastry, Spanish milhoja, or Portuguese empanadilla; though such preparations are not universally considered puff pastries. Puff pastry differs from phyllo (filo) pastry, though puff pastry can be substituted for phyllo in some applications. Phyllo dough is made with flour, water, and fat and is stretched to size rather than rolled. When preparing phyllo dough, a small amount of oil or melted fat (usually butter) is brushed on one layer of dough and is topped with another layer, a