In a small pot over medium low heat, add the peanut butter, maple syrup, coconut oil, and salt. Stir until melted and combined. Turn heat off and add the protein powder. Stir until well combined and smooth.
In a large bowl, add the cornflakes and peanut butter mixture. Stir and mix until everything is evenly combined.
Line a 9x5 loaf pan with parchment paper. Transfer the cornflake mixture into the pan and press down firmly and evenly.
Make the chocolate topping by adding the chocolate, peanut butter, and coconut oil to a bowl. Microwave in 30 second increments, stirring after each increment, until melted.
Pour chocolate over the top of the peanut butter cornflakes. Place in the freezer for at least 1 hour to set. Sprinkle flaky sea salt on top (optional), slice, and enjoy! Store leftovers in the freezer.