Preheat the oven to 180°C (static heat). Place a 26 x 36 cm frame on a baking tray covered with baking paper. Beat the eggs, sugar and salt in a food processor mixing bowl for five minutes until it is all pale and creamy. Add the sunflower oil and milk and mix everything together briefly.
Finely grate the apples and stir them quickly into the dough. Sieve the flour and baking powder into the dough and blend everything into a smooth paste.
In a separate bowl, mix the double cream cheese, the low-fat curd cheese, sugar, vanilla extract and egg with a whisk. Sieve the cornflour into the mix and stir everything together. Fill an icing bag with the cream and curd cheese mix and attach a small star-shaped nozzle. Squeeze the topping over the dough in diamond shapes and bake for 25 minutes in the lower third of the oven.
After baking, let the dough cool under a clean tea towel and dust with icing sugar.