Step 1: Prepare the Mixture

1. Melt Butter and Marshmallows: In a large saucepan over low heat, melt the unsalted butter and mini marshmallows, stirring constantly until smooth.
2. Add Peanut Butter: Stir in the peanut butter until fully combined.
3. Mix in Protein Powder: Remove the saucepan from heat and mix in the protein powder and vanilla extract until well combined.

Step 2: Combine with Cereal

1. Add Rice Krispies: Gently fold in the Rice Krispies cereal until evenly coated with the marshmallow mixture.

Step 3: Press into Pan

1. Prepare the Pan: Line an 8×8 inch (or similar size) baking dish with parchment paper for easy removal.
2. Press Mixture: Transfer the mixture into the prepared baking dish. Use a spatula or your hands (lightly greased) to press the mixture down firmly and evenly.

Step 4: Cool and Cut

1. Optional Topping: If using chocolate chips, sprinkle them on top while the mixture is still warm and gently press them in.
2. Cool: Allow the treats to cool at room temperature for about 30 minutes until set.
3. Cut into Squares: Once cooled, lift the treats out of the pan using the parchment paper and cut into squares.