Line an 8x8 or 9x9 baking pan with parchment paper.
In a large pot, melt the butter over medium heat.
Stir in the cocoa powder until combined (use a whisk if your cocoa powder is clumpy).
Add 6 cups of marshmallows (leaving one cup to the side!) and stir with the melted butter until the marshmallows have melted. Add in the vanilla extract and chocolate chips and give them a quick stir (no need to melt the chocolate chips completely).
Add in the rice krispie cereal and remaining cup of marshmallows. Stir quickly until combined.
Pour the rice krispie mixture into your lined pan and use a greased spatula or your hands to gently press the mixture down into an even layer. Sprinkle with sea salt, mini chocolate chips, or sprinkles if desired.
Video
Notes
Doubling Instructions: Double all ingredients and use a 9x13 dish.Marshmallows: Large marshmallows can be used instead of mini ones. When stirring in the remaining 1 cup, be sure to cut or chop those marshmallows into smaller pieces first before adding them in with the rice krispies.Storage Instructions: Store in an airtight container for up to 3 days.