Chill all ingredients. If unsalted butter is not available, wash the butter well in ice water. Reserve 1 tablespoon of the butter. Shape the remaining butter into a flat cake 1 inch thick.
Blend the 1 tablespoon of butter into the flour and moisten to a stiff dough with the ice water and cognac. Knead it on a lightly floured board until smooth and elastic, about 2 minutes. Cover and let rest a few minutes.
Roll into a rectangle about ¼ inch thick, using as little flour on the board and the rolling pin as possible. Place the butter in the center of the lower half of the pastry, sprinkling lightly with flour. Fold upper half over. Press edges firmly together. Fold ends over, pressing tightly. Let stand 5 minutes. Roll very lightly to the original shape and thickness. Fold again.
PASTRY MUST BE CHILLED WELL BEFORE EACH ROLLING. Try wrapping pastry in a towel and plunging it into a pan of cracked ice. Handle dough as little and as quickly as possible.
Line baking sheet or sheets with double thickness of waxed paper. Cut pastry in desired shapes. Bake in a preheated 425° oven about 15 minutes. Fill or top with your choice of the recipes in this section, or in the Breads, Rolls, Muffins and Rusks Section, or with a favorite of your own.