Beat the butter until foamy, mix in 150 g of sugar with the vanilla sugar. Separate 2 eggs into yolks and whites. Mix the flour with the cornstarch and baking powder. Stir the egg yolks with the whole eggs into the butter mixture. Add the flour mixture.
Preheat the oven to 180 ° C (top / bottom heat). Line a box cake tin (30 cm long) with baking paper. Pour the batter into the mold. Beat the egg whites until stiff. Sprinkle in the remaining sugar. Mix in the ground nuts and lemon juice. Make a wide groove lengthways in the batter and add the nut mixture.
Bake the cake in the oven on the lower rack for 70 minutes. If necessary, cover with aluminum foil after 45 minutes so that it does not get too dark. Do the cooking test with a wooden stick. Let the nut cake stand in the switched-off oven for another 10 minutes, then take it out of the mold and let it cool down on a wire rack.