Roughly chop the chocolate and melt it with the butter. Let cool down. Wash, peel and dice the apples. Drizzle with the lemon juice.
Mix eggs, sugar, vanilla sugar and salt until creamy. Fold in the chocolate mixture. Stir in the flour, baking powder and the apple cubes.
Grease a rectangular shape (35 x 23 cm), pour in the dough and smooth it out. Bake in the preheated oven (fan oven: 150 ° C, top / bottom heat: 175 ° C, gas: level 2) for about 40 minutes.
For the glaze, mix the ingredients with the mixer to a smooth, slightly liquid glaze and distribute evenly on the cake.