Preheat oven to 360 degrees F /180 degrees C. Grease a small rectangular pan (approximately 5 x 3,5 inches) and line it with a sheet of parchment paper.
In a small bowl combine flax seed meal and water. Mix until smooth. These are the flax seed eggs.
In another bowl combine flour and baking powder. Mix to blend.
Drain the black beans but keep the water as it will be added separately to the mixture.
In a food processor combine the drained beans, cocoa powder, coconut oil, dates, brown sugar, flax seed eggs and vanilla extract. Pour about half of the drained bean water and process until smooth. Pour some more of the water, if needed, so the mixture becomes like a thin cake batter.
Transfer the mixture to a big bowl. Fold the dry ingredients and the chocolate chips into the brownie batter, until absorbed.
Pour into the prepared pan and bake for about 40 minutes or until a toothpick inserted in the centre comes out just with few crumbs.
Let cool for 30 minutes before serving. Alternatively serve the brownies refrigerated.
Store in airtight container in the fridge.
*Normally in Europe the cans are 400 g and in US they are 15 oz.**You can substitute the dark brown sugar by same quantity of coconut sugar, maple syrup, xylitol or agave syrup.