Preheat the oven to 180 degrees Celsius.
Sift the cocoa, brown rice flour, baking powder and baking soda into a bowl. Follow this with the brown sugar. Set aside.
In a large bowl, combine the plant milk and vinegar, and allow to sit for 5 or so minutes, to form a buttermilk. Add in the coconut yoghurt and whisk to combine. Add in the pumpkin puree, and do the same.
In a small bowl, add the psyllium husk, tapioca flour and boiling water, and whisk to combine. Once it has combined, add the oil and continue to whisk until it is incorporated. Set aside.
If your buttermilk mixture is particularly cold, gently heat it over a small saucepan of water. You'll be pouring raw chocolate into the mixture, so it might seize up if it's particularly cold. You can always gently heat the mixture if this happens.
Whisk in the raw chocolate until the batter is uniform. Next, add the psyllium husk egg, and whick vigorously until the batter is smooth.
Add the maple syrup and sea salt flakes, and whisk to combine. Add the coffee and the dry ingredients, and continue mixing until a batter has formed.
Pour the mixture into a 23 x23cm tin, greased with olive oil. Cook for 30 minutes, or until a skewer comes out clean.