Preheat your oven to 350°F (175°C). Line an 8x8-inch baking pan with parchment paper, leaving some overhang on two sides to lift the brownies out later. Lightly grease the exposed sides of the pan with oil or cooking spray.
1 8x8-inch baking pan, cooking spray or oil
Pour the black beans into a colander and rinse under cool running water for at least 30 seconds, stirring with your hand, until the water runs clear. Let them drain very well so no excess water sneaks into the batter.
1 can (15 ounces) black beans
Add the drained black beans to a food processor or blender. Add the oil, nut or seed butter, maple syrup, coconut sugar (if using), vanilla, and 2 tablespoons of non-dairy milk. Blend on high until the mixture is very smooth and glossy, scraping down the sides as needed. If the mixture is too thick to blend, add up to 1 more tablespoon of non-dairy milk; the consistency should be like thick chocolate pudding.
1 can (15 ounces) black beans, 3 tablespoons neutral-flavored oil, 1/4 cup creamy nut or seed butter, 1/3 cup pure maple syrup, 2 tablespoons coconut sugar, 2 teaspoons pure vanilla extract, 2-3 tablespoons non-dairy milk
To the same food processor or blender, add the cocoa powder, baking powder, baking soda, and salt. Pulse several times, then blend again until everything is fully combined and the batter is thick, smooth, and shiny. If you can still see pieces of bean skin, blend a bit longer.
1/2 cup unsweetened cocoa powder, 1/2 teaspoon baking powder, 1/4 teaspoon baking soda, 1/4 teaspoon fine sea salt
Carefully remove the blade. Stir in the chocolate chips and chopped nuts, if using. If your blender jar is too tight to stir in the mix-ins easily, transfer the batter to a mixing bowl first, then fold in the chips and nuts. The batter will be thick, more like cookie dough than cake batter.
1/2 cup dairy free dark chocolate chips or chunks, 1/4 cup chopped nuts
Scrape the thick batter into the prepared pan. Use a spatula to spread it evenly into the corners and smooth the top. If you like, sprinkle a few extra chocolate chips on top and gently press them into the batter. A damp spatula or slightly wet spoon can help smooth the surface without sticking.
1 8x8-inch baking pan, 1/2 cup dairy free dark chocolate chips or chunks
Bake on the center rack of the oven for 20–25 minutes. Start checking at 18–20 minutes. The edges should look set and just begin to pull away from the pan, and the center should look set but still slightly soft and glossy. A toothpick inserted in the center should come out mostly clean with a few moist crumbs, not wet batter.
Set the pan on a wire rack and let the brownies cool completely, at least 30–45 minutes. Use the parchment overhang to lift the brownies out of the pan. Slice into 9 large squares or 12–16 smaller squares. For extra fudgy texture and deeper flavor, chill the cooled brownies in the fridge for 1–2 hours before serving.