Pre-heat the oven, 175˚C / 350˚F, fan bake. Line a square baking tin with baking paper.
Open the tin of chickpeas over a blender to save the liquid, using a sieve to catch the chickpeas. Transfer the chickpeas to a food processor.
Over a double boiler, melt the 100g dark chocolate together with the vanilla and coconut oil.
Pour the melted chocolate mixture over the chickpeas in the food processor, and add raw cacao powder, sea salt and baking soda. Blitz until the chickpeas are evenly processed. Set aside for the moment.
Blend the chickpea liquid on high until foamy, then add coconut sugar and blend again. Pour this over the mixture in the food processor, add almond meal and oat flour, and pulse until you have a medium-thickness brownie batter.
Pour batter into lined baking pan, scatter over a handful of chocolate chips if desired, place on the middle rack in the oven and bake for 30 minutes, allowing to cool completely before cutting.