Defrost the puff pastry sheets. Cut apples into slices. Bring lemon juice, apple juice and 1 teaspoon sweetener to the boil in a large pan. Steam apple slices for about 5 minutes. Take out, drain and let cool down.
Place puff pastry sheets on top of each other and roll out on a floured work surface. Cut out a circle (30 cm Ø). Grease a pizza or quiche dish (26 cm Ø). Place the dough inside and press down the edges. Prick the base several times with a fork. Put apple slices on the dough. Mix sour cream, eggs, 5 teaspoons diabetic sweetener, lemon peel and vanilla pulp. Pour over the apples. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) on the lower shelf for approx. 30 minutes. Remove and let cool off.
Put apple slices on the dough. Mix sour cream, eggs, 5 teaspoons diabetic sweetener, lemon peel and vanilla pulp. Pour over the apples. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) on the lower shelf for approx. 30 minutes. Remove and let cool off. Sprinkle the rim with 1 teaspoon of diabetic sweetness. Decorate cake with apple slices and lemon balm