Wash, peel and grate apples. Sprinkle with 2 tablespoons of lemon juice. Separate the eggs. Beat egg whites, 6 tablespoons of ice-cold water, sugar and vanillin sugar until stiff. Mix flour, poppy seeds, hazelnuts and apples.
Carefully fold in the egg yolks first, then the poppy seed mixture. Line the bottom of a springform pan (26 cm Ø) with baking paper. Fill in sponge mixture and smooth it down. Bake in a preheated oven (electric: 200 °C/ gas: level 3) for about 30 minutes.
Then allow to cool slightly, remove from the rim, turn out of the mould and allow to cool completely. For the icing, stir icing sugar, remaining lemon juice and rum until smooth. Spread evenly over the cake.
Results in about 12 pieces. Serve decorated with some crème fraîche and almond slivers.