In a Dutch oven,melt butter over medium heat. Add marshmallows;cook and stir until melted. Remove from heat. Stir in cereal and 2 cups Oreos. Press into a greased 13x9 -in. Baking pan.

Spread melted baking chips over top. Sprinkle with remaining Oreos,pressing gently to adhere. Cool to room temperature. Cut into bars.