1. Start with the vanilla custard for the filling. Mix the cornstarch, sugar, and vanilla extract with a little of the milk until smooth. Add the remaining milk and the heavy cream to a saucepan and bring to a boil. As soon as you can see the bubbles come up, add the cornstarch mixture and stir in. Let cook for a moment while stirring constantly until nicely thickened. Remove from the heat and let cool down for a moment, then add the egg yolk and mix in. Set aside and keep stirring from time to time to prevent skin from forming on top of the custard.

2. Peel and quarter the apples, remove the cores, and cut into small cubes. Add the apples together with the lemon juice, water, cinnamon, and cornstarch to a large saucepan/pot and mix to combine. Let the apples simmer over medium heat for about 6-8 minutes until the apple pieces are softer but not mushy. Remove from the heat, remove excess liquid from the saucepan, then add the custard and mix well. Set aside.

3. Preheat the oven to 340°F (170°). Line a 9.5-inch (24cm) springform tin with baking parchment and grease lightly. Set aside.

4. Add the flour for the dough to a large bowl and mix with the baking powder, sugar and salt. Add the quark, milk, oil, and vanilla extract and mix (quickly) to create a soft and smooth dough. You can use a handheld mixer (with dough hooks) or a simple wooden spoon to mix everything. Transfer the dough to the prepared springform tin and press to the bottom and sides to create a nice base. The dough should be at least 1.6 inches up on the sides of the baking tin.

5. Add the apple custard filling and spread evenly. Sprinkle the almonds and some coarse sugar on top and bake the cake for about 70-75 minutes. The edges of the cake should have a nice golden color, but make sure the almonds are not getting too dark. Cover the cake with a piece of baking parchment if necessary. Take the cake out of the oven and let cool down completely inside the springform tin. When cooled down, remove from the tin and place on a serving plate. Dust with some confectioners’ sugar (optional) and serve with whipped cream or additional vanilla sauce.