My Moist Poppy Seed Eierschecke, Just Like From the Pastry Shop

Ingredients

1 ¼ cups150 gall-purpose flourIn German recipes plain flour means soft wheat flour Type 405 unless stated otherwise. In the US use all-purpose flour; in the UK, plain flour.
6 tbsp80 gunsalted butterGerman butter is unsalted and has about 82 percent fat. In the US use unsalted butter (European-style unsalted butter is closest); in the UK, unsalted butter.
¼ cup50 ggranulated sugar
1large egg yolkSave the egg white.

2 cups500 mlmilk
1 packetcustard pudding powder1 packet = about ⅓ cup (37 g). A packet of flavored starch that is cooked with 2 cups (500 ml) of milk and sugar into a thick pudding. In the US use about ⅓ cup (40 g) cornstarch plus 1 tsp vanilla extract per packet; in the UK, custard powder, about 40 g per German packet (it is unsweetened, so it swaps 1:1 by weight).
1 ⅔ cups400 gquarkAny fat content works. German quark is a fresh, mild and slightly tangy cheese with a spoonable texture. In the US use full-fat Greek yogurt strained overnight, or farmer's cheese; in the UK, quark from the supermarket chiller (choose a full-fat one if you can find it).
17 ½ oz500 gpoppy seed fillingStore-bought or homemade (see below). A ready-to-use sweet filling of ground poppy seeds. In the US use canned poppy seed filling from the baking aisle or an Eastern European shop; in the UK, poppy seed filling from a Polish or Eastern European shop.
⅓ cup70 ggranulated sugar

3large egg yolks
4large egg whites
⅔ cup80 gpowdered sugarVery finely ground sugar for icings and dusting. In the US use powdered sugar (confectioners' sugar); in the UK, icing sugar.
¾ cup plus 1 tbsp200 gquark

14 oz400 gpoppy seedsGround. German recipes use blue poppy seeds and grind them first for fillings. In the US and the UK, grind poppy seeds in a spice grinder.
2 tbsp30 gunsalted butter
5 tbsp70 mlmilk
3 to 5 tbspgranulated sugar

For the shortcrust pastry, knead all the ingredients into a dough and press it into a 10-inch (26 cm) springform pan. Leave the sides bare and only cover the bottom.
For the poppy seed filling, warm all the ingredients together on the stove for a few minutes until the butter has melted. Let it steep and cool for at least 30 minutes.
Mix all the ingredients for the quark layer together and spread the mixture over the shortcrust base in the pan.
Bake in the preheated oven at 350°F (170°C) convection (fan) for about 30 minutes, until the top is golden brown. At this point the filling still wobbles when you move the pan. While it bakes, prepare the topping.
Mix the egg yolks & quark together. Beat the egg whites with the powdered sugar until stiff. Then fold the beaten egg whites into the quark mixture in 3 to 4 portions.
Carefully spread the topping over the hot bottom part of the Schecke and smooth it out. Put it back in the oven and bake for about 20 to 30 minutes more, until the topping is nicely browned. The Schecke still wobbles at this stage too! By now it should also have risen really high and look like a cloud. That changes a lot as it cools, though.
The Schecke is best enjoyed chilled, after dusting it with powdered sugar.

From German Pastry Chef. Full recipe with photos: germanpastrychef.com/recipes/poppy-seed-eierschecke/