And, may I add, that it is completely worth every second.
"He pops it into a 450 ° oven and closes the door. Consider carefully now. There are 257 layers of paste in that cookie, separated by 256 layers of butter . . . But every one of the thin sheets is full of water. Consequently, when, after eight minutes or so, the heat of the oven raises the temperature of the layers above 212 °, the water expands violently into steam. Since. however, the steam is entrapped, it forces the layers apart to make a means of escape--a task made easy now, for the butter has melted and each layer of paste is nicely free of the others . . . At this point he turns the oven down slightly and waits until all the steam is driven out and all the layers have been french-fried by the intervening butter. The triumph of puff paste is complete."
(The Supper of the Lamb, 1967, p. 158)