1. Check the blackberries for bad ones and remove them. Rinse the berries and let them drain.

2. Add the cornstarch, sugar, and vanilla extract for the pudding to a small bowl and mix with a little milk until well combined. Pour the remaining milk into a saucepan and bring it to a boil. As soon as you can see bubbles starting to rise, add the cornstarch mixture and stir it in. Let the pudding cook for a moment (while stirring constantly) until it has thickened nicely. Remove the saucepan from the heat and let the pudding cool for about 5 minutes, then add the egg yolk and stir it in. Set aside until ready to use – stirring occasionally to prevent a skin from forming.

3. Preheat the oven to 180°C (350°F) fan-forced. Line a 20cm springform tin* with baking parchment and set aside.

4. For the streusels, add flour, sugar, ground hazelnuts, and salt to a large bowl. Add the butter in small pieces. Next, add the egg and vanilla extract and mix them in. We always use a fork or spoon first until the egg is reasonably well combined with the flour – then we use our hands to create different-sized streusels.

5. Transfer about 2/3 of the streusels to the prepared springform tin and press them to the bottom and sides – you want the dough going at least two fingers wide up the sides. Next, pour the pudding into the baking tin and spread it evenly. Add the drained blackberries on top first, then the streusels. Sprinkle the cake with some additional coarse sugar(optional) and then bake it for about 36-40 minutes in the lower third of the preheated oven. At the 20-minute mark, sprinkle the sliced hazelnuts on top and continue baking the cake. Remove the finished cake from the oven and let it cool down completely on a wire rack. Serve with whipped cream.