HEAT oven to 350°F. Coat 9 x 13-inch baking pan with no-stick cooking spray. Combine cookie mix, butter and egg in large bowl. Stir until smooth. Press evenly into prepared pan.
BAKE 24 to 26 minutes until edges are golden brown. Cool completely in pan on wire rack. Crumble cooled cookie into extra-large bowl. Stir in frosting and cream cheese. Beat with electric mixer on low speed until evenly blended.
LINE a 15 x 10-inch baking pan with wax paper. Roll cookie mixture into 1-inch balls. Place on prepared baking pan. Chill 30 minutes. Place white baking chocolate in microwave-safe bowl. Microwave on HIGH for 30 seconds. Stir. Repeat until mixture is smooth. Reheat as needed while coating the cookie balls. Dip cookie balls in mixture to coat, allowing excess to drip off. Immediately sprinkle with decorator sprinkles. Repeat with remaining cake balls. Chill for 1 hour or until coating is set.