Preheat your oven to 350°F and line the base of a 9 or 10-inch springform pan with parchment paper. Grease the sides of the pan.

Mix flour, ground almonds, sugar, vanilla sugar, baking powder, and salt in a bowl. Add in the egg and butter, kneading until you have a smooth dough. Set aside 1/3 of the dough for the streusel topping. Roll out the remaining dough on a floured surface and press it into the prepared pan, creating a rim about 1.5 inches high. Chill in the refrigerator for at least 30 minutes.

Prepare the rhubarb by removing leaves and ends, peeling if needed, and slicing into 0.2-inch thick pieces. Grate the lemon zest and juice half the lemon. Rub the zest into the sugar.

In a bowl, mix quark, sour cream, pudding powder (or cornstarch), and the aromatic sugar. Add the lemon juice, then mix in the eggs and melted butter.

Pour the cheesecake filling into the dough-lined pan and arrange the rhubarb slices on top.

Combine the chopped almonds with the reserved dough and sprinkle over the cheesecake to create the streusel topping.

Bake for 50-60 minutes. Let the cheesecake cool in the oven with the door slightly open, then refrigerate until ready to serve.