1. Spray a 9 x 13-inch baking pan with nonstick spray.
2. Melt the butter and chocolate in a large saucepan over low heat. Add the marshmallow cream, cocoa, and vanilla; stir until smooth. Remove from heat and add the cereal, stirring until well coated.
3. Spread the mixture into the prepared pan. Spray your hands with nonstick spray and press the batter down evenly. Let cool 10 minutes, then cut into 24 squares.