In a bowl, combine the protein powder, butter, maple syrup, and oat flour. Slowly add milk, stirring until the mixture becomes doughy and can be molded. Line a loaf pan with parchment paper and press the mixture firmly into the bottom. Place the pan in the freezer while you make the middle layer.
In a small saucepan over low heat, stir together peanut butter, maple syrup, and milk until smooth and creamy. Remove from heat, add the protein powder, and stir until the mixture is thoroughly blended and creamy. Spread evenly over the bottom layer in the loaf pan.
Freeze the pan for 20 minutes to allow the layers to firm up.
Melt dark chocolate chips using short microwave intervals (stir between each) or in a double boiler. Pour the melted chocolate over the middle layer. Tilt the pan as needed for an even coating.
Place the pan back in the freezer for another 20 minutes or until the chocolate sets. Slice into bars and store in the fridge.
