Preheat the oven to 350°F. Lightly oil or coat an 8 X 8-inch baking pan with nonstick cooking spray and set aside.
Place the black beans in the bowl of a food processor; process until smooth and creamy. Add the eggs, oil, sugar, cocoa powder, vanilla extract, peppermint extract as desired, baking powder, and salt and process until smooth. Add ¼ cup of the chips and pulse a few times until the chips are incorporated.
Pour the batter into the prepared pan and sprinkle the top with the remaining ¼ cup chocolate chips.
Bake 30 to 35 minutes, or until the edges start to pull away from the sides and a toothpick inserted in the center comes out clean. Cool in the pan before cutting into 2-inch squares.
Makes 16 servings. Source: No Whine with Dinner- 150 healthy, kid-tested recipes by Liz Weiss and Janice Newell Bissex, 2011.