Line 2 half-sheet pans with parchment paper. Dust the work surface well with flour. Place the dough on the work surface with the open seam of dough facing you. Dust the top of the dough with flour. Using a large, heavy rolling pin, roll out the dough into a 16 by 12-inch rectangle. Don't press the dough too hard; let the weight of the pin do much of the work. If you changed the position of the dough while rolling, it is important to keep track of which side contains the seam.
Turn the dough with the seam facing you. (If you've lost track, look carefully at the sides of the dough, and you should be able to discern it, even though it is faint.) Using a pizza wheel and a yardstick, neatly trim the rough edges. Cut the dough in half lengthwise to make two 16 by 6-inch rectangles. Fold each rectangle into thirds, place on a half-sheet pan, and refrigerate uncovered for about 15 minutes.
Remove the dough strips from the refrigerator. Work with one dough strip at a time. Using a pizza wheel, starting at the top left corner of one strip, cut down to make a half-triangle with a 2-inch base; set aside. Measure 3 1/2-inches from the top left corner of the strip and mark a notch with the wheel at this point. Cut down diagonally from the notch to meet the bottom left edge of the dough strip to make another triangle with a 3 1/2-inch base. Continue cutting, alternating diagonal cuts, to cut out 6 triangles. The last cut will also yield a half-triangle with a 2-inch-wide base. Repeat with the second strip of dough to make 6 more large triangles and 2 half-triangles. You should have a total of 12 large triangles and 4 half-triangles.
Place a single "complete" triangle on the work surface with the base of the triangle facing you. Stretch the bottom slightly so it is about 5-inches wide. Pick up the triangle. With one hand, hold the dough triangle at the bottom and stretch it with your other hand until it is about 7-inches long. Return the triangle to the work surface. Starting at the bottom, roll up the triangle, and finish with the tip underneath the croissant on the pan. Curve the croissant by bringing the 2 ends together and then cross one end over the other, and press together. Repeat rolling the remaining dough triangles, placing them 1 1/2-inches apart on the pan. Overlap 2 of the half-triangles at their long sides, and press the seam together. Roll up as described for the large triangles and add to the pan. Repeat with the remaining half-triangles.
Choose a warm place in the kitchen for proofing. Slip each pan into a tall "kitchen-sized" plastic bag. Place a tall glass of very hot water near the center of each pan. Wave the opening of each bag to trap air and inflate it like a balloon to create "head room," being sure that the plastic does not touch the delicate dough. Twist each bag closed. Let stand until the croissants look puffy but not doubled, 1 1/2 to 2 hours.
Meanwhile, position racks in the center and top third of the oven and preheat to 375 degrees F. Remove the glasses from the bags, then the pans. Lightly brush the croissants with the beaten egg. Bake for 10 minutes. Reduce the heat to 350 degrees F and continue baking until the croissants are crisp and golden brown, about 15 minutes longer. Serve warm or cool to room temperature.
Croissant Dough Recipe