Beat the fat, sugar and cinnamon in a bowl with the whisk of the hand mixer until creamy. Stir in the eggs one after the other. Mix flour and baking powder and stir into the dough. Pour the dough into a greased springform pan (20 cm Ø) sprinkled with flour.
Wash apple, grate dry, cut out core with an apple corer and cut apple into thin slices. Spread on the dough. Chop hazelnuts coarsely and sprinkle over the cake. Bake in a preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: see
manufacturer) Bake for 40-45 minutes.
Warm the jam. Remove the cake from the oven and spread with jam. Let cool on a cake rack. Whipped cream tastes good with it.