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 hours.
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.
Decorate the cookies:
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.