Combine flour, baking powder and salt in a bowl; set aside. In mixer bowl, beat butter and sugar until fluffy, 3 min. Beat in yolks and vanilla. Add flour mixture and combine. Wrap dough in plastic wrap, chill 2 hour.
Heat oven to 350°F. Roll dough to ¼ inch thick on a floured surface. Cut using a 2-by-3½-inch raindrop cutter to cut 18 cookies. Use a 1½-inch round cutter to cut 18 cookies. Place drops and circles on separate baking sheets. Cut each circle in half and separate. (Dough scraps can be re-rolled up to 2 times.)Bake cookies until just golden, about 15 min for drops, about 10 min for cut circles. Cool completely.
Color ⅔ cup Royal Icing red and ¼ cup each pink and blue and place in pastry bags with tips. Fill another pastry bag with 1¼ cup white icing.
Ice tops of drop cookies with red icing and bottoms and all half-circles with white icing. Allow icing to set, about 30 min. Adhere half circles to drop cookies with icing to form a mustache. Pipe hat trim and tip with white icing. Pipe eyes and nose with blue and pink icing. Allow icing to set completely, at least 3 hrs.
There are so many things that make these Santa face cookies special. The little blue eyes and pink nose give Santa's face a little sweet personality. The up-turned mustache helps Santa smile, and they are perfect for packing up in cellophane bags for party favors or gifts. Because the royal icing sets, it won't smear or rub off once the cookies are dry.