Crank your oven to it's highest setting. Line a rectangular tin approx 16x26cm (6x10in) with baking paper.

Place black beans, cocoa, brown sugar and oil in a large jug or bowl. Using your stick blender puree the beans (or you can do this in a food processor) or mash beans with a fork until as smooth as possible. Add eggs and vanilla and mix until well combined.

Pour the mixture into your tin. Sprinkle over the chocolate chips.

When the oven is preheated. Pop the brownies in the oven. Bake for 10 minutes or until puffed up a little and set in the middle - you want these brownies cooked through. They should feel springy.

Cool in the tin for at least an hour but preferably longer before cutting into squares. You can speed up the process by refrigerating. Cut into 12 pieces.