Warm the milk until lukewarm. The temperature should be between 95 and 110 degrees Fahrenheit, basically body temperature or a tad warmer. Add in the yeast and let sit until bubbly, for about 10 minutes.
200 milliliters milk, 10 grams active-dry yeast
In the meantime, in a large bowl (or the bowl of a stand mixer), combine the flour, salt and sugar.
500 grams all-purpose flour, 1 pinch sea salt, 75 grams granulated sugar
Add in the bubbly yeast-milk mixture, room temperature butter and eggs. Add in the lemon zest if using. Knead the dough on low until smooth, about 8 minutes.
75 grams unsalted butter, 2 eggs, ½ lemon
Cover airtight (or use a damp kitchen towel over the top), and let rest in a warm spot for about 30 minutes. The dough should have increased in size by 50 percent.
In the meantime, get the poppy seed filling ready. Combine the milk and butter in a small saucepan and heat until boiling. Then remove from heat and stir until the butter is dissolved. Stir in the poppyseeds and sugar and set aside.
60 milliliters milk, 30 grams butter, 125 grams poppy seeds, 40 grams granulated sugar
Knead the dough briefly, then roll it out into a 60 by 50 cm (or 24 by 20 inch) rectangle. Spread on the poppy seed filling. Fold the long side in half, creating a 30 by 50 cm (or 12 by 20 inch) rectangle with the filling in the middle.
Cut into 3 long strips and braid with the poppy seed filling facing out or up. Fold under the ends to achieve a more consistent braid look and stretch out and push together any sections that need it. Place onto a baking sheet covered with parchment paper or reusable silicone baking mats. Cover loosely with a clean linen towel and allow to rest in a warm spot for half an hour. In the meantime, preheat the oven.
Transfer to a baking sheet prepped with parchment paper or a reusable silicone baking mat, and allow to rise for another 15 minutes. Meanwhile, preheat your oven to 320 degrees Fahrenheit (160 degrees Celsius) on the convection setting.
Brush on the egg-milk wash, sprinkle with pearl sugar (can leave it off), and bake on the middle rack for about 30 to 35 minutes. Cover your Hefezopf with some aluminum foil for the last 10 minutes of baking, so it doesn't get too dark.
1 egg, 3 Tablespoons milk, pearl sugar
Remove from oven and let cool for about 30 minutes before cutting up and serving. I love eating it with butter.