Puff pastry is made with flour, butter, water, and salt. In the traditional method, the flour, water, salt, and a small amount of the butter are combined to make a dough, and then the remaining butter is pounded with a rolling pin between sheets of wax paper to create a thin square sheet of butter. This butter square is then wrapped in the dough, and then the entire thing is rolled out into a long rectangle and folded into thirds like a letter. The dough is then refrigerated for a while, then rolled and folded again, refrigerated, rolled and folded... 6-7 total cycles of rolling, folding, and refrigerating! This creates hundreds of thin layers of dough and butter, which, when baked, puff and form the ultra-thin, crispy layers.
Cook's Illustrated's quick method has you combine the flour, salt, and a bit of the butter just like the original, but then you add the remaining butter to the food processor and the water, pulsing to make a dough that still has visible chinks of butter in it. You roll this dough out and fold it longways into thirds, and then roll it up like a jellyroll, so that the rolls create the many layers. This is chilled just once, and then you can use it.
A napoleon consists of a sheet of puff pastry which is baked sandwiched between two sheet pans to keep it from rising too much. This is then cut longways into 3 equal pieces. The top piece gets glazed with poured fondant traditionally (blech!) or as I like it - with chocolate ganache and a drizzle of melted white chocolate. All the pieces are stacked with pastry cream between.
Quick Puff Pastry (from Cook's Illustrated)
2 cups (9 oz) unbleached all purpose flour
20 tablespoons very cold unsalted butter, cut into 1/4 inch cubes
1 tsp salt
6-7 tablespoons ice water
Place the flour and salt in the bowl of your food processor. Pulse once or twice to combine. Add 4 tablespoons of the butter and pulse 10 times. Add the remaining butter and pulse twice just to evenly distribute the butter. Add 6 tablespoons of the water and pulse 4 times. Press the dough between your fingers to see if it will hold together. If it's too dry to form a dough, add the remaining tablespoon of water 1 teaspoon at a time, pulsing once and rechecking to see if it will hold together between additions. Turn out the dough onto a floured countertop and knead as briefly as possible to form a rough ball of dough. Roll the dough out to a 12 by 18 inch rectangle. Fold it in thirds longways, so you have a 4 by 18 inch rectangle. Start at the short end and roll it up like a jelly roll. Pat it down a but to form a 5-inch square. Wrap with plastic wrap and refrigerate for 1 hour before using.