Preheat your oven to 350°F (175°C). Line an 8x8-inch (20x20 cm) baking pan with parchment paper, leaving an overhang on two sides to lift the brownies out later. Lightly grease or spray the parchment.
In a small bowl, stir together the ground flaxseed and water. Let sit for 5–10 minutes, until thickened and gel-like.
3 tablespoons ground flaxseed, 6 tablespoons water
Add the rinsed black beans, flax mixture, maple syrup, coconut sugar, nut butter, melted coconut oil, vanilla, and optional coffee to a blender or food processor. Blend until very smooth and creamy, scraping down the sides as needed so no visible bits of bean remain.
1 can (15 oz / 425 g) black beans, 3 tablespoons ground flaxseed, 6 tablespoons water, 1/2 cup (120 ml) pure maple syrup, 1/4 cup (50 g) coconut sugar, 1/4 cup (60 g) creamy nut butter, 1/4 cup (60 ml) melted coconut oil, 2 teaspoons pure vanilla extract, 1–2 tablespoons strong brewed coffee or espresso
Add the cocoa powder, rolled oats, baking powder, baking soda, and salt directly to the blender or food processor. Blend again until the batter is thick, smooth, and glossy. The batter will be thicker than traditional boxed brownie batter.
1/2 cup (45 g) unsweetened cocoa powder, 1/3 cup (30 g) rolled oats, 1/2 teaspoon baking powder, 1/4 teaspoon baking soda, 1/4–1/2 teaspoon fine sea salt
Remove the blade if using a food processor. Stir in the dairy-free chocolate chips by hand with a spatula so they stay intact and chunky.
1/2 cup (85 g) dairy-free chocolate chips
Transfer the batter to the prepared pan. Use a spatula to spread it evenly into the corners and smooth the top. Sprinkle a handful of extra chocolate chips on top if desired.
Bake at 350°F (175°C) for 22–28 minutes. Start checking around 22 minutes. The edges should look set, the top slightly dry and crackly, and a toothpick inserted near the center should come out mostly clean with a few moist crumbs but no wet batter.
Place the pan on a cooling rack and let the brownies cool fully, at least 45–60 minutes. They firm up significantly as they cool. Once cool, use the parchment overhang to lift the slab out of the pan and cut into 12–16 squares.
Serve as-is, or top with a sprinkle of flaky sea salt, coconut whipped cream, or fresh berries for a fancier dessert.