Preheat your oven to 180 degrees Celsius (350 degrees Fahrenheit). In a large mixing bowl, combine the flour, sugar, and baking powder, whisking them together to eliminate any lumps. Add the room temperature butter and use your fingertips to rub it into the dry ingredients until the mixture resembles coarse crumbs. Crack in the eggs and mix gently until just combined, ensuring you maintain a light texture throughout.

Carefully fold in the ground poppy seeds to your dough, ensuring they are evenly distributed without forming clumps.

Take a 9-inch springform pan and grease it lightly with butter or baking spray to prevent sticking. Transfer the dough into the prepared pan, pressing it down gently and evenly across the base.

Place the springform pan in your preheated oven and bake for about 30 minutes, or until the top is golden brown and a toothpick inserted into the center comes out clean. Once baked, remove the cake from the oven and allow it to cool completely in the pan on a wire rack before adding the filling.

While your cake base cools, prepare the vanilla quark cream by mixing the quark, milk, vanilla sugar, and lemon zest in a medium bowl until smooth and creamy.

Once your cake base has cooled completely, pour the creamy vanilla quark mixture evenly over the top. Use a spatula to spread it out smoothly.

Cover the assembled cake with plastic wrap and place it in the refrigerator to chill for at least 2 hours or until the vanilla quark cream is firm and set.

After chilling, carefully release the springform pan and slice the Poppy Seed Crumble Cake into wedges. Serve it with fresh berries or a dusting of powdered sugar.