Begin by lining a 9x9 inch baking dish with parchment paper, leaving some overhang for easy removal.
In a large mixing bowl, combine the PB Fit powdered peanut butter, collagen peptides, and sugar-free powdered sugar. Use a spatula to mix until well combined.
Add the peanut butter, vanilla extract, and nonfat milk to the dry mixture. Stir until you achieve a thick, creamy batter.
Transfer the mixture into the prepared baking dish. Use the spatula to evenly spread and press down the mixture.
In a microwave-safe bowl, add the semi-sweet chocolate chips. Microwave in intervals until melted and smooth.
Pour the melted chocolate over the pressed peanut butter mixture. Spread it evenly across the top.
Place the baking dish in the refrigerator for at least 1 hour or until the chocolate is set and the bars are firm.
Once set, lift the bars out using the parchment overhang. Slice into squares and enjoy!