Preheat oven to 350F. Line an 8x8 inch baking dish with parchment paper.
Mash banana with a fork in a large mixing bowl and measure to ensure you have ½ cup. Add peanut butter, maple syrup, egg or flax egg, and vanilla. Whisk well to combine.
Add cocoa powder, baking soda, and salt if your peanut butter is unsalted. Whisk to combine then stir in in chocolate chips.
Pour batter into prepared baking dish. Top with a few more chocolate chips and flaky salt if you're feeling fancy. Bake for 27-28 minutes, or until a knife comes out with a few crumbs. Do not over-bake! Let brownies cool in pan on a wire rack for at least 30 minutes (or ideally until fully cooled) before slicing. These are amazing right out of the refrigerator, too!
