Begin by preparing approximately 6-7 cups of popcorn using your preferred method, whether it's stovetop, microwave, or an air popper. If using the stovetop, heat a few tablespoons of oil in a large pot and add the kernels, covering with a lid. Keep the heat medium-high, shaking occasionally until popping slows, then transfer it to a large mixing bowl.

In a large saucepan, melt 4 tablespoons of butter over low heat. Once melted, add in regular-sized marshmallows, stirring continuously for about 5-7 minutes until the mixture is completely smooth and glossy.

Remove the saucepan from heat and stir in a teaspoon of vanilla extract and the optional cake batter protein powder, mixing until fully combined.

Pour the gooey marshmallow mixture over your freshly popped popcorn, using a spatula to gently fold and coat each kernel evenly.

Once coated, immediately sprinkle a generous amount of Funfetti sprinkles over the popcorn mixture. Toss again to distribute the sprinkles evenly throughout the popcorn.

Transfer the coated popcorn mixture into a parchment-lined baking dish, pressing it down firmly into an even layer using a spatula or your hands that have been lightly coated with cooking spray.

Allow the Funfetti Marshmallow Popcorn to cool at room temperature for about 30 minutes. Once set, slice it into squares or break it into clusters.