Ingredients:

1 package fudge brownie mix (13-inch x 9-inch pan size)
1 package (10½ ounces) miniature marshmallows
2 cups (12 ounces) semisweet chocolate chips
1 cup peanut butter
1 tablespoon butter
1½ cups crisp rice cereal

Method:

Prepare the brownie batter according to package directions for fudge-like brownies. Pour the batter 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 the cereal and spread over brownies. Refrigerate for 1-2 hours or until firm before cutting.
Source: Food.com