Butter a 13-by-9-inch baking dish.
Add the butter, marshmallows, and cocoa powder to a large saucepan. Place over medium heat and stir until melted, about 5 minutes. Stir in the cereal until combined. Press into the buttered baking dish. Drizzle with the melted white chocolate. Let cool, and then cut into bars.
Recipe courtesy of The Neelys