Peel, core, and chop apples, cooking with water and lemon juice until tender (10-15 mins). Stir in sugar and cinnamon, then puree if desired. Set aside to cool.

In a mixing bowl, combine flour, butter, sugar, vanilla sugar, baking powder, and salt. Work into a smooth dough, add egg, and knead until soft.

Line a baking tray with parchment, press 2/3 of the pastry into the tray.

Spread applesauce over the pastry base evenly.

Roll out remaining pastry, covering applesauce and sealing edges.

Preheat oven to 200°C (392°F) and bake for 30-40 mins until golden.

Whisk powdered sugar and lemon juice for the glaze, adjust consistency.

Once cake cools, drizzle glaze on top and allow to soak.

Cool completely before slicing and serving.