In a medium bowl with a rubber spatula stir peanut butter and egg, add dry ingredients, stir until it is almost homogenous, add the water and vanilla to help you get a smoother batter, stir until you have a creamy and thick batter.
Use an 8” iron skillet, spray with oil and add brownie batter.
Bake for 17 minutes or until is no longer wet.
Remove from the oven and let it cool for 3 minutes. Serve warm or cold depending on your preference. Store any leftovers in the fridge.