Prepare brownie batter according to package direction. Stir in 1 cup malted milk balls. Spread into a greased 13 x 9 x 2 inch baking pan.
Bake at 350 degrees for 30 minutes. Cool completely on a wire rack.
In a small saucepan, melt chocolate chips and butter over low heat. Remove from heat. Stir in milk and vanilla. Spread over brownies. Sprinkle with the remaining malted milk balls. Refrigerate for 10-15 minutes or until set.