Preheat your oven to 180℃/350°C (fan forced).
In a large bowl, blender or processor, mix together the sweet potato, butter or oil, sweetener, eggs and vanilla until combined.
Add the cacao, bicarbonate of soda and baking powder and combine.
Finally, stir in the coconut flour. Coconut flour absorbs a lot of liquid so you should only need the two tablespoons. Your batter should be the consistency of a very thick, airy (cake like) batter. Let it sit for a minute and if it still seems a little wet, add more coconut flour teaspoon by teaspoon.
Line a small slice tin with baking paper.
Pour the batter into the tin and top with the raspberries or cherries (optional).
Bake for 25 minutes or until the centre is firm to touch or a skewer inserted comes out clean. Cool completely before slicing. It will firm up once chilled.
Store in the fridge in an airtight container or you can also freeze them.
Enjoy at room temperature or warm with double cream or coconut cream and fresh berries.