Lightly butter or spray a 9x9 baking dish with cooking spray. Set aside.
Heat butter in a large heavy bottomed pot over medium heat until completely melted. Save the butter wrapper for later.
Add most of the marshmallows, reserving 2 cups for later and reduce the heat to low. Stir until the marshmallows are completely melted, then remove from the heat.
Add cocoa powder, chocolate chips, vanilla, and salt. Stir until combined and the chocolate chips have melted.
Add rice krispies and reserved marshmallows. Stir until the cereal is evenly coated in the marshmallow mixture. Pour into the prepared pan and gently press with the reserved butter wrapper.
Let set up for 15 minutes before slicing into squares.
