Beat yolks with 40 g sugar and 1-2 tablespoons (30 g) water until foamy. Beat the egg whites with the remaining sugar until stiff and fluffy, then mix the yolks with the beaten egg whites. Sift the flour with the cocoa powder and stir into the mixture. Stir in the oil very carefully in a thin stream so that the mixture does not collapse when stirred. Butter a cake pan, sprinkle with flour and pour in the mixture. Bake in the preheated oven at 150 °C and after half the baking time increase the heat to 170 °C (bake for a total of 45-50 minutes). Process further as desired (fill with jam or creams and/or glaze).