Separate eggs. Beat the fat, 125 g sugar, vanillin sugar, lemon zest and salt until fluffy. Gradually stir in the egg yolks and milk. Beat the egg whites until stiff, adding 125 g of sugar. Fold the beaten egg whites into the fat-sugar mixture. Mix flour, starch and baking powder and fold in.
Pour the dough into a greased, flour-polluted box form (approx. 2 litres capacity; 10 x 30 cm). Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) on the 2nd rack from below for 45-50 minutes. Remove from the oven, allow to cool for approx. 15 minutes and turn out of the tin. Leave to cool completely. Dust with icing sugar and cut into pieces
waiting time approx. 2 hours