Heat oven to 350°F.
Beat dry cake mix, egg and 1-1/2 cups COOL WHIP in large bowl with mixer until blended. (Dough will be stiff.) Stir in 1/2 cup chocolate chips.
Shape dough into 24 balls, using about 1 Tbsp. dough for each ball.
Place, 2 inches apart, on parchment-covered baking sheets.
Bake 8 to 9 min. or just until edges of cookies are firm. (Do not overbake.) Cool 2 min. Remove cookies to wire racks; cool completely.
Microwave remaining COOL WHIP and 1 cup of the remaining chocolate chips in microwaveable bowl on HIGH 1-1/2 min. or until chocolate chips are completely melted and mixture is well blended, stirring after 1 min. Cool 5 min.
Spread COOL WHIP mixture onto cookies; sprinkle with remaining chocolate chips..
