Line a 9-inch square baking pan with parchment paper.
In a large bowl, mix the crispy rice cereal with the confectioners' sugar and protein powder.
In another small bowl, whisk the melted butter with the peanut butter and vanilla extract. Add the peanut butter mixture to the cereal mixture and stir until the cr
umbs are evenly moistened. Pour the mixture into the prepared pan and press into an even layer.
Refrigerate until firm, 30 to 45 minutes.
Cut into 16 even squares. Store the bars in the refrigerator in an airtight container until ready to serve.