Prepare brownie batter according to package directions for fudge-like brownies. Pour into greased 13-in. x 9-in. baking pan
Bake at 350° for 28-30 minutes. Top with marshmallows; bake 3 minutes longer (marshmallows will not be completely melted). Cool on a wire rack.
In a microwave-safe bowl, melt the chocolate chips, peanut butter and butter; stir until smooth. Stir in cereal; spread over brownies. Refrigerate for 1-2 hours or until firm before cutting. Yield: 2-1/2 dozen.