1. Preheat the oven to 350°F (180°C). Line a baking sheet with baking parchment, place an adjustable baking frame* on top, and adjust it to a size of about 12×9 inches. Set aside.

2. For the streusels, add the spelt flour, cane sugar, and baking powder to a large bowl and mix to combine. Add the soft butter, vanilla extract, and the egg – mix with the dough hooks of a hand mixer until you get different-sized streusels. Add about 2/3 of the streusels to the prepared baking frame and press down to create an even layer. Pre-bake the cake base for about 15 minutes. Remove from the oven and let cool down for a moment. Reduce the temperature of the oven to 340°F (170°C).

3. While the cake base is pre-baking, prepare the filling and topping. Mix the quark with sugar, cornstarch, eggs, vanilla extract, and lemon zest in a large bowl. Set aside. Wash and dry the rhubarb (do not peel it, only where necessary), then cut it into small pieces. Mix with the raspberries, sugar, and lemon juice and set aside.

4. Spread the quark mixture on the slightly cooled cake base, distribute the rhubarb mixture evenly on top, and sprinkle with the remaining streusels and some sliced almonds. Bake the cake for about 55-60 minutes – the streusels should get a nice golden color. Remove from the oven and let cool down completely before slicing into pieces.