Lightly flour a cool, clean surface. Roll the dough out into an 18 x 10" rectangle. Using a pizza cutter, slice the dough in half lengthwise, so you have two 5 x 18" rectangles. Slice the dough in half the opposite way, giving you four 5 x 9" rectangles. Then slice each in half again, so you have eight 5 x 4.5" squares. Slice each square diagonally.
Gently stretch each of the triangles out slightly. Roll the croissants, starting at the wide end, and curve the sides in slightly.
Spray a baking sheet lined with foil with non-stick cooking spray. Arrange the croissants on the pan and leave a little room between them because they will expand in the oven. You may need a second pan if they don't all fit on one.
Allow the croissants to rest for 1 hour in the fridge before baking them.
Make the egg wash: Mix 1 egg + 1 tablespoon of milk in a small bowl. Brush each of the croissants with the egg wash before baking.
Bake the croissants in the preheated oven for 20 minutes. Halfway through baking rotate the pan, which helps make sure they brown evenly. Remove the croissants from the oven and serve warm. Croissants are best fresh out of the oven, enjoy!