Grease a 9x13 pan or line with parchment paper. Set aside.
Add butter to a large pot. Heat on low until fully melted.
Add marshmallows to the butter. Stir constantly on low heat until smooth and glossy. No lumps.
Remove the pot from heat. Add the Ascent Fruity Cereal Whey Protein. Stir fast and thoroughly until fully combined. The mixture will thicken. Keep stirring until smooth.
Pour in puffed rice cereal and fruity cereal. Fold gently until everything is coated evenly.
Transfer mixture to the prepared pan. Lightly press down using a spatula or wax paper. Do not pack it tight or they turn dense.
Let cool for 30 minutes at room temperature. Slice into squares and serve.
