Preheat oven to 160°C (320°F) and lightly grease a 12"x8" baking dish
Mix flaxseeds with warm water in a bowl and set aside to set
Melt the coconut oil and set aside to cool slightly
In a food processor or blender, blend the black beans, milk and flax mixture until smooth
In a large bowl, mix the flour, sugar, cocoa powder, salt, baking powder, and bicarbonate of soda
Add the bean mixture, vanilla extract, melted coconut oil, and maple syrup to the dry ingredients and mix well
Transfer the batter into the greased baking dish, even the top with a spatula
Bake for around 20 minutes until the top is firm but the inside is still gooey
Serve with greek yoghurt, berries or on its own
