Preheat oven to 350.
Grease a 9X9 pan. Puree undrained black beans in food processor until smooth. Combine with brownie mix until smooth.
Pour into pan. Bake according to instructions on box. Mine took about 38 minutes to be slightly under-cooked (which is how I like them).
You can not tell the difference in taste. You are also adding ZERO fat to the mix. In comparison, egg and oil adds about 6.5 grams. Give it a try! Kid approved 🙂