Line a baking sheet with parchment paper. Spray the parchment paper with cooking spray and set aside.
Heat a large skillet or pot over low-medium heat.
Add butter and stir until melted.
Add marshmallows and stir frequently until melted.
Quickly stir in protein powder! If you don't stir quickly, the marshmallow and marshmallow mixture will thicken.
Quickly stir in the rice krispies. Start by pouring about ½ of the rice krispies, stirring, and then pouring the remaining rice krispies. Again, stir quickly before the mixture thickens!
Press the rice krispie mixture onto the baking sheet.
Optional: Add sprinkles or drizzle chocolate as a topping.
Let sit for about 30 minutes.
Use a knife to cut. Enjoy!