Preheat oven to 200 C/ 425 F
Wash the beetroots thoroughly under cold water to remove any traces of dirt. Leave at 2-3 cm of stalk at the top and the root tail intact.
Place the beetroot on a baking tray and drizzle with the sunflower oil.
Roast for 90 minutes, turning every 20-30 minutes, until the beetroot is tender. A knife will slide in and out of the beetroot easily when it is ready.
Remove from the oven and allow to cool completely.
When cooled, the skin will slip off. Discard the skin, top and bottom, and place the whole beetroot in a blender. Puree. You will likely need to use the blender tamper to keep things moving.
Preheat oven to 180 C/ 350 F. Line a 12-hole cupcake tin with large paper cupcake cases.
Blend the cacao nibs in your high powered blender until they form a powder.
Sift the flour, ground cacao nibs and bicarbonate of soda into a large bowl. You may have some cacao which won't fit through the sieve, just chuck it in the bowl along with the rest and stir in the sugar.
Break the dark chocolate into small pieces in a heat proof bowl and suspend over a pan of barely simmering water. Usually I boil the kettle, pour it into a pan, place the bowl on top and leave it off the heat, stirring once or twice, until it has melted.
If using the butter, add the butter along with the chocolate to melt. If using oil, add the oil along with the eggs after the chocolate has melted.
Stir 250 grams of room temperature roasted beetroot into the dry ingredients along with the chocolate mixture. Stir until just combined.
Spoon into the paper cupcake cases. They will be full, but rest assured it will be ok.
Bake for 25-30 minutes in the centre of the oven until a skewer, inserted into the centre of a cake comes out clean.
Transfer to a wire rack to cool completely.
To make the frosting, sift the icing sugar into a bowl and beat with the softened butter, milk and beetroot puree until it reaches the desired consistency. I use a food processor for this.
Using a plastic disposable piping bag, pipe swirls of frosting on the top of the cupcakes. Decorate with cocoa nibs.
Store in an airtight container. Cupcakes will keep lovely for a few days.