Melt butter in a large pot over medium heat.
When the butter is melted, add peppermint marshmallows and stir until melted.
Remove from heat. If you want an extra kick of mint, add about 1/4 teaspoon of peppermint extract.
Add Cocoa Krispies to the marshmallow mixture and stir until thoroughly coated.
Press mixture into a 9x13 pan (or a 9x9 pan for thicker squares).
Add chips or sprinkles (or both!) sprinkled over the top of the krispie squares and press in lightly. Allow to cool before cutting.