1. Roll refrigerated sugar cookie dough to an 1/8-inch thickness on a lightly floured surface; cut with a (3- x 5-inch) mitten cookie cutter, and place dough on parchment paper-lined baking sheets.
2. Bake cookies at 350° for 8 to 10 minutes or until edges are lightly browned. Cool cookies completely on wire racks.
3. Tint half of ready-to-spread vanilla frosting with blue food coloring gel to desired shade. Spread frosting evenly on cookies.
4. Spoon remaining half of frosting into a 1-qt. zip-top plastic bag. (Do not seal.) Snip a tiny hole in 1 corner of bag, and pipe decorative designs on cookies. Sprinkle with edible glitter. Garnish, if desired.