1 Heat oven to 325°F. Spray bottom only of 9-inch pie plate with cooking spray.
2 In large bowl, mix cookie mix, 1/2 cup softened butter and egg with spoon until soft dough forms. Stir in candy sprinkles. Press dough in bottom of pie plate.
3 Bake 33 to 38 minutes or until center is set and edges are golden brown. If needed, cover edges of cookie with foil to keep from overbrowning. Cool completely, about 1 1/2 hours.
4 In medium bowl, beat powdered sugar, 3 tablespoons softened butter, the vanilla and 3 teaspoons of the milk with electric mixer on low speed until smooth and creamy. If necessary, add additional milk to make frosting easy to spread.
5 Spread frosting over cookie pie. Decorate top of frosted cookie as desired with assorted holiday candies. To serve, cut into wedges.