Prepare the pan by lining a 9x9 inch baking pan with parchment paper or aluminum foil, extending over the edges. Lightly grease to prevent sticking.

In a small bowl, whisk together milk and vanilla protein powder until smooth. Set this mixture aside.

In a large pot over medium heat, melt salted butter, stirring continuously until fully melted.

Reduce heat to low and add mini marshmallows, stirring until fully melted and smooth. Add vanilla extract and milk mixture, mixing well.

Remove from heat and stir in Rice Krispies, mixing until evenly coated. Avoid over-mixing.

Pour mixture into prepared baking pan, spreading it evenly. Press down gently without packing too tightly.

Let cool at room temperature for 30-60 minutes before slicing into squares.