Step 1 In the bowl of a food processor, combine the flour, powdered sugar and salt. Add the butter, pulsing until the dough comes together.
Step 2 Remove the dough and divide in half. Shape each half into a log about 1 1/2 inches in diameter, rolling in waxed paper. Chill the dough until firm enough to slice, at least 30 minutes.
Step 3Heat the oven to 350 degrees, and line 2 baking sheets with parchment. Pour the red sugar into a small bowl or baking dish to a thickness of about one-half inch.
Step 4Cut each dough log into one-half-inch rounds. Press each round lightly onto the sugar to coat, then place, sugar side up, onto the parchment-lined baking sheet 1 to 2 inches apart. Sprinkle a few white crystals on top of each cookie for added sparkle. Use the blunt end of a skewer or similar item to make 2 indentations for "buttonholes."
Step 5Bake the cookies for 8 minutes, then reverse the sheets and continue to bake until the cookies are golden on the bottom (no coloring on top), 8 to 12 minutes longer. Cool on racks.