combined. Cover and chill for 2 to 3 hours. On a floured surface, roll dough to a 1 cm thickness. Using envelope as a pattern, cut shapes in dough with a sharp knife. Reroll dough scraps. Cut out 3 cm squares of dough to resemble stamps. Transfer letters and stamps to unprepared baking sheet with a spatula. Using a paintbrush, paint, addresses, postmarks, and stamps with Edible Decorator Paint. Allow each color of paint to dry thoroughly before painting with additional colors. Bake cookies for 25 to 30 minutes, removing stamps if they start to brown. Cool slightly and remove from baking sheet. Cook completely. Prepare powdered sugar icing and attach stamps to letters. To make Edible Decorator Paint, mix egg yolk with half teaspoon water. Divide mixture into several small cups. Add paste food coloring as desired. If needed, add additional water, 1 drop at a time, to make paint the consistency of ink. Use thin coats of the paint. Allow each color to dry before proceeding with next color. In recipes using opaque or pastel paint, add white, paste or liquid, food coloring. This improves opaqueness and removes much of the yellow color of the egg yolk. Food painted with paint should be returned to the oven for a few minutes to set the paint and cook the egg yolk. ----