Puff pastry

Puff pastry, also known as , is a flaky light pastry made from a laminated dough composed of dough (') and butter or other solid fat ('). The butter is put inside the dough (or vice versa), making a "" which is repeatedly folded and rolled out before baking.
The gaps that form between the layers left by the fat melting are pushed (leavened) by the water turning into steam during the baking process. 
History.
Puff pastry seems to be related to the Greek phyllo, and is used in a similar manner to create layered pastries. Puff pastry appears to have evolved from thin sheets of dough spread with olive oil to laminated dough with layers of butter. 
While traditionally ascribed to the French painter and cook Claude Lorrain who lived in the 17th century (the story goes that Lorrain was making a type of very buttery bread for his sick father, and the process of rolling the butter into the bread dough created a croissant-like finished product), the story is spurious. In fact, the origin of modern puff pastry appears to be Spanish, perhaps through Arab or Moorish influences: the first known recipe of modern puff pastry (using butter or lard) appears in the Spanish recipe book "Libro del arte de cozina" ("Book on the art of cooking") written by Domingo Hernández de Maceras and published in 1607. Maceras, the head cook in one of the colleges of the University of Salamanca, already distinguished between filled puff pastry recipes and puff pastry tarts, and even mentions leavened preparations. Thus, puff pastry appears to have had widespread use in Spain by the beginning of the 17th century. The first French recipe of puff pastry was published in François Pierre La Varenne's "Pastissier françois" in 1653.
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 formula_2 is the number of finished layers, formula_3 the number of folds in a single folding move, and formula_4 is how many times the folding move is repeated. For example, twice-folding (i.e. in three), repeated four times gives formula_5 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/Portuguese milhoja, or 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 process repeated as often as desired. When the phyllo bakes it becomes crispy, but since it contains somewhat less water, does not expand to the same degree as puff pastry. Puff pastry also differs from Austrian strudel dough, or Strudelteig, which more closely resembles phyllo.