• Preheat the oven to 350º F and place a rack in the center of the oven.

Poppyseed Filling

• In a sauce pot, whisk together the milk, sugar, and poppyseeds. Place over medium heat and cook, whisking regularly until thickened and bubbling.
• Once it starts to bubble, sprinkle in the semolina while whisking. Continue to cook until thick, switch to a rubber spatula to stir until necessary.
• Remove from the heat and pour the poppyseed filling into a shallow dish, stir in the lemon zest.
• Allow the mixture to cool to room temperature. Stir in the quark, followed by the egg, and stir to combine.

Streusel

• In a medium bowl, whisk together the flour and sugar. Then add in the butter and vanilla.
• Use a fork or your fingers to rub the butter into the dried ingredients until fully combined and no dry bits remain.

Crust

• Press a large square of parchment paper into a 7" springform pan and crease the excess along the edges so that it lays flat.
• In the bowl of a stand mixer, add in the butter, sugar, and vanilla. Use the paddle attachment to beat the ingredients together on medium speed until combined.
• Scrape down the sides of the bowl and then add in the flour.
• Mix once more until no more dry ingredients are visible.

Assemble & Bake

• Pour the mixed crust into the lined springform pan. Press the crust into the the base of the pan and just barely up the sides.
• Be sure that the corner where the sides and bottom meet isn't too thick. You can do this by pressing the back of your pointer finger into the corner once the crust has been pressed into the whole pan.
• Carefully pour the filling into the pressed crust. Crumble the streusel over the top.
• Bake the mohnkuchen for 30 minutes, then rotate the pan 180º and bake for another 10-20 minutes until golden brown.
• Once baked, remove the mohnkuchen from the oven and leave to cool on a rack until it is room temperature. Then, move it to the fridge and allow it to set fully before removing the springform pan.
• Leave to set in the fridge for at least 4 hours or up to overnight. Top with a dusting of powdered sugar before serving.