Preheat the oven to 425 F/ 220 C/ gas mark 7. Place the beets on a baking tray and bake for 45 minutes. Remove from the oven, leave to cool, then peel. Chop the beets roughly, combine with the desiccated coconut and puree until smooth. Set aside. (you can bake the beetroot ahead and, once cooled, refrigerate it until you are ready to use it)
Preheat the oven to 350 F/ 180 C/ gas mark 4. Lightly grease a 23 cm square baking pan, line with baking paper and set aside.
Break up the chocolate into small pieces, place, along with the coconut oil, in a bowl over a pot of simmering water (the water shouldn't touch the bowl) and melt, stirring often. Remove from the heat when there are still a few chocolate pieces visible and stir until completely melted. Set aside. Alternatively melt the chocolate and coconut oil in the microwave.
Combine the flour, baking powder and cacao (or cocoa) powder, stir with a whisk and set aside.
In another bowl beat the eggs and sugar for 1-2 minutes until fluffy. Stir in the beet mixture, then gradually pour in the melted chocolate (it will have cooled by then), stirring all the time with a spoon. Add the flour mixture and stir just to combine.
Pour the batter into the pan, smooth over the top with a spatula and bake in the centre of the oven for 28 minutes. Remove from the oven, let cool in the pan for 15 minutes, then lift out of the pan with the paper and place on a cooling rack.
Make ahead: The beetroot can be baked ahead and, once cooled, refrigerated (covered) until you are ready to use it (best to use it the following day). Puree the beetroot when you are ready to make the recipe.
Cacao or cocoa: I usually prefer to use cacao rather than cocoa powder, as cacao is healthier, but it's absolutely fine to use cocoa powder instead. (You might also like this collection of 27 everyday healthy cacao recipes)
Batter: Do not overmix the batter, stir just to combine.
Storing: Once completely cooled store the brownies in an airtight container and refrigerate for up to 3 days. Pop in the microwave for a few seconds before serving if possible.
Freeze for up to 3 months.
Preparation time includes the time needed to prepare the beetroot.