Roughly dice the beetroot and put it together with the oil in a high mixing bowl. Puree finely with a hand blender. Add the eggs one after the other and stir in with the whisk of the hand mixer. Mix flour, baking powder, cocoa, sugar, vanillin sugar and salt. Add the vegetable-egg mixture and mix to a smooth dough
Grease a box cake tin (2.5 litres capacity, 30 cm long) and dust with flour. Pour in the dough and smooth it down. Bake in the preheated oven, 2nd rail from below (electric oven: 175 °C/ convection oven: 150 °C/ gas: level 2) for approx. 1 1/4 hours. Cover with aluminium foil for the last 15-20 minutes
Let the cake cool in the mould on a cake rack for 20-30 minutes. Then turn out of the mould, let it cool down and dust with cocoa powder
waiting time approx. 2 hours