Preheat oven to 350°F (180°C). Grease and/or line a 9x9-inch (23x23 cm) baking pan with parchment paper and set aside.
Place beans and 1 Tbsp (15 mL) warm water in a large bowl. Using a potato masher or a sturdy fork, mash the beans until they are smooth as possible. Add an additional 1 Tbsp (15 mL) water if needed to get the desired texture. Don't worry if there are a few tiny bits, they'll disappear when we bake!
Add melted butter to the beans and mix together until you have a fairly smooth batter.
Add brown sugar and mix well.
Add eggs, mix well, then add vanilla and whip until the batter is smooth. Set aside.
In a separate bowl, whisk together the flour, baking powder, and salt. Add chocolate chips and stir again until the chips are coated with the flour mixture.
Add the dry ingredients to the wet ingredients, mixing until just combined.
Pour batter into prepared baking pan and spread evenly. Sprinkle a few more chocolate chips on top, if desired.
Bake for 25-30 minutes, or until the edges are golden brown and a toothpick comes out mostly clean.
Let them cool completely in the pan before you even think about slicing them, this part is the hardest, but it's worth the wait!