Line a 9x9 inch baking pan with foil or parchment paper and grease it to prevent sticking.

Whisk together the milk and vanilla protein powder until smooth in a medium mixing bowl.

Melt the salted butter in a large pot over medium heat, stirring occasionally.

Once the butter is melted, reduce heat to low and add the mini marshmallows, stirring continuously until fully melted.

Incorporate the vanilla extract and the protein mixture into the melted marshmallows until well combined.

Remove from heat and fold in the Rice Krispies cereal until evenly coated.

Pour the mixture into the prepared pan, spreading evenly and pressing lightly. Allow to cool for 30-60 minutes.