Grate the manioc finely and soak in a bowl full of water twice over for 20 minutes each time. Throw the deposit away. Whisk the eggs together with the sugar. Add the softened butter, whipping continually. Add the vanilla sugar and the rum. Mix together with the grated manioc and the baking powder. Put the mixture in a deep sandwich tin and bake in a hot oven for about 45 minutes. The cake should be browned.