Roast the almonds in a dry pan without fat until golden brown. Take them out and let them cool down. Wash the lemon hot, dab dry and finely grate the peel. Squeeze the lemon. Peel, quarter and core apples.
For larger apples, halve the quarters again lengthwise. Drizzle half of the lemon juice over the apples. Line the roaster (approx. 25 x 35 cm) with baking paper, preheat the oven (electric cooker: 180 °C).
Separate eggs. Set aside the egg white. Whisk butter and 300 g sugar with the whisk of the mixer until the mixture is almost white. Mix in first the egg yolks one by one, then vanilla sugar, cinnamon, 1 pinch of salt, lemon peel and the rest of the juice.
Stir in flour and almonds briefly.
Beat the egg whites until stiff, adding 50 g sugar. Fold the beaten egg whites into the dough in 3 portions with the dough scraper. If too much is stirred, the dough will collapse and the cake will not rise.
Smooth the dough in the roaster. Place the apple pieces next to each other on top and press in lightly. Bake in a hot oven for 20 minutes. Then switch the oven down to 160 °C and continue baking for about 30 minutes (test with a chopstick!), covering with aluminium foil after 15 minutes if necessary.
Let the cake cool down with the oven door slightly open. Dust with icing sugar.