Start by melting the butter in a large pot over low heat.
Add chocolate chips and cocoa powder to the butter. Stir until the chocolate is completely melted and smooth.
Remove 1 cup of marshmallows from the package and set it aside. Pour the remaining marshmallows into the pan and stir until all of the marshmallows have melted.
Measure the rice krispies cereal into a large bowl and pour the chocolate mixture over it. Stir until all of the cereal is covered in chocolate.
Spray a 9x13 baking dish, or a Jelly Roll pan with nonstick cooking spray. Or, line with a parchment paper sheet.
Use a greased spatula to press the Chocolate Rice Krispy mixture until it covers the bottom of the pan.
Allow the treats to set for at least an hour, before cutting into bars.