Preheat the oven to 175°C/350°F. Line a 20 × 11 cm loaf pan with baking paper, leaving some overhang on the sides.
Rinse the cooked beans thoroughly and leave them to drain for 10–15 minutes. Pat them dry if they still appear wet.
Add the coconut sugar to a food processor and blend briefly until the crystals become finer. Transfer it temporarily to a small bowl.
Melt the dark chocolate and coconut oil together over a bain-marie or in the microwave in 15–20-second intervals, stirring after each interval. Set aside to cool slightly.
Add the drained beans, blended coconut sugar, maple syrup, 20 ml of soy milk and vanilla extract to the food processor. Blend until completely smooth, stopping several times to scrape down the sides.
Add the almond flour, cocoa powder, baking powder and salt. Blend briefly until evenly combined.
Pour in the melted chocolate and coconut oil. Blend again until the batter is smooth, dark and glossy. It should be very thick but creamy. If necessary, add the remaining soy milk one teaspoon at a time, without exceeding 30 ml in total.
Transfer the batter to the prepared pan. Use a spatula to spread it evenly into the corners and level the surface.
Bake on the middle shelf for 30–35 minutes. The edges should be set and a toothpick inserted into the centre should come out with moist crumbs but no raw batter.
Leave the brownies in the pan for 30 minutes. Lift them out and transfer them to a cooling rack. Allow them to cool completely for at least 2 hours before slicing.