Mix the semi-fat butter, sugar, vanilla sugar and eggs until frothy. Sift flour and baking powder and fold in. Preheat the oven to 180 degrees. Grease a springform pan (26 cm) and sprinkle with breadcrumbs.
Pour 2/3 of the batter. Peel and core the apples and cut into fine wedges. Spread on the dough. Sprinkle with a little sugar and cover with the rest of the batter. Bake the cake for about 45 minutes.