1Heat oven to 375°F. In medium bowl, stir cookie mix, flour, softened butter and egg until soft dough forms.
2On floured surface, roll dough to about 1/4-inch thickness. Cut with 2 1/2- to 3-inch cookie cutters. On ungreased cookie sheets, place cutouts 1 inch apart.
3Bake 7 to 9 minutes or until edges are light golden brown. Cool 1 minute; remove from cookie sheets. Cool completely, about 15 minutes.
4Spread frosting on cooled cookies. Decorate as desired with decorator sugar crystals. Store cookies in tightly covered container.