1. Combine the flour and sugar for the base in a large bowl. Add the cold butter in small pieces, along with the egg, and quickly knead everything into a smooth dough. Line a 25/26cm springform tin* with baking parchment. Roll out the dough on a lightly floured surface into a circle that’s slightly larger than the springform tin. Place it in the baking tin and press it firmly onto the bottom and up the sides – the edge should be at least 3cm high. Place in the fridge until needed again.

2. Combine the flour and sugar for the streusels in a bowl. Add the cold butter in small pieces and mix everything to get different-sized streusels – this works best by rubbing everything between your fingers. Add the rolled oats and mix in. Place in the fridge until needed.

3. Clean the rhubarb and peel it if necessary, then cut it into small pieces. Set aside about 200g of the rhubarb in the fridge for later. Add the rest to a small saucepan together with the brown sugar and bring to a boil. Reduce the heat and let the rhubarb cook for about 2-3 minutes. The rhubarb should soften slightly, but not fall apart. Remove from the heat and let cool down.

4. Preheat the oven to 180°C (350°F). Melt the butter for the filling and let it cool down slightly.

5. In a large bowl, mix the quark, cream cheese, melted butter, vanilla extract, and the eggs until smooth. Mix the sugar and cornstarch, then add to the bowl and stir in.

6. Take the springform tin with the base out of the fridge, sprinkle the breadcrumbs over the base, and then evenly distribute the cooked (and cooled) rhubarb on top. Pour the quark mixture over the rhubarb, then sprinkle the remaining rhubarb from the fridge as well as the streusels on top. Bake the cake in a preheated oven for about 65-75 minutes – the streusels should have a golden brown color. Remove the cake from the oven and let it cool completely inside the baking tin on a wire rack. Dust the cake with some confectioners’ sugar to your liking before serving (optional).