Preheat the oven to 350-degrees F. Line an 8” brownie pan with parchment paper in both directions, using metal clips to hold the sides.
In the bowl of a food processor (or blender), add the beans, baking powder, salt, brown sugar, vanilla and melted butter. Blend until very smooth, about 1 minute. Scrape down the sides and blend again, if necessary.
Add the flour and pulse to combine, scraping down the sides to ensure it’s all incorporated.
Add the egg and pulse lightly to combine.
Spread the mixture into the prepared pan (it will be very thick!) and bake on the center rack for 15 minutes. It’s done when a toothpick inserted comes out only barely moist or with slightly wet crumbs, but not overly liquid-y.
