Preheat oven (electric cooker: 175 °C/circulating air: 150 °C/gas: see manufacturer). Grease a cupcake mould (approx. 2.5 l capacity; approx. 25 cm Ø) and dust with flour.
Cut the woody ends off the beetroot if necessary. Cut the tubers into pieces. Finely mash the beetroot and oil with a hand blender. Stir in the eggs one by one.
Mix 275 g flour, baking powder, cocoa, sugar and vanilla sugar. Add the puree and mix to a smooth dough.
Fill the dough into the mould. Bake in the preheated oven for 45-50 minutes. Let the cake rest in the form for about 10 minutes. Then turn out onto a cake rack and let it cool down. Dust with icing sugar and cocoa.