Combine all ingredients except chips in a good food processor and blend until completely smooth.
Really blend well. (A blender can work if you absolutely must, but the texture—and even the taste—will be much better in a food processor.)
Stir in the chips, then pour into a greased 8×8 pan. Optional: sprinkle extra chocolate chips over the top.
Cook the black bean brownies 15-18 minutes, then let cool for at least 10 minutes before trying to cut. If they still look a bit undercooked, you can place them in the fridgeovernight and they will magically firm up! Makes 9-12 brownies.
The trick with these: serve them first, and then reveal the secret ingredient.