Preheat oven to 150 °C Line a baking dish with baking paper.
Melt chocolate
Break up 100 g dark chocolate. In a medium pot add ¼ cup olive oil, ¼ cup maple syrup and chocolate, and gently heat over medium heat, stirring frequently, until chocolate is melted. Set aside to cool slightly.
Prep beans
While the chocolate mixture is cooling, drain and rinse 400 g black beans. Add to a processor, and blend until very smooth, scraping down the sides when needed.
Make brownie
Pour the chocolate mixture into the food processor along with 1 tsp baking powder, 2 eggs and 1 tsp vanilla extract and blend until smooth and well combined, scraping down the sides when needed to ensure all ingredients are well blended. Pour the mixture into the prepared baking dish. Sprinkle 1 cup berries over the top.
Bake brownie
Bake for 20-25 minutes, until it is mostly set around the edges, but still slightly soft in the middle. Set aside to cool for 5 minutes, then refrigerate for about 20 minutes to set.
To serve
Once cool, slice into 24 pieces with a long sharp knife. Store in an airtight container. Serve as is, or warm with a dollop of Greek yoghurt or ice cream.