Quarter apples, cut out core. Cut the fruit flesh into fine slices and sprinkle with lemon juice. Beat butter and 125 g sugar until creamy. Stir in eggs one by one. Mix flour, cornstarch, baking powder and ground hazelnuts. Alternately stir in flour mixture, ricotta and milk. Pour into a greased springform pan (20 cm Ø) sprinkled with hazelnut leaves.
Arrange the apple slices according to colour in a ying-yang pattern and press in lightly. Decorate with hazelnut kernels to separate the colours. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for about 40 minutes. After 30 minutes sprinkle with 2 tablespoons of sugar. Leave to cool slightly while still in the mould. Remove from the mould and allow to cool completely