1. Mix the milk, sugar, and yeast in the bowl of a food processor until the yeast has completely dissolved. Cover and let the yeast work for about 10 minutes.

2. Next, add the spelt flour, salt, and egg yolk to the bowl and knead for about 5-6 minutes using the dough hook attachment until you get a smooth dough. Gradually add the butter in small pieces, waiting each time until the previous piece has been incorporated well before adding more. When the butter has been fully incorporated, continue kneading the dough for about 6 minutes longer. Cover the dough with a damp cloth and let it rise in a warm place for about 1 hour.

2. Add about 200ml (6.7 fl. oz.) of the milk to a small saucepan together with the poppy seeds, sugar, and vanilla extract – combine the remaining milk with the cornstarch and set aside. Heat up the milk and poppy seeds in the saucepan while stirring constantly, bring the mixture to a boil, then add the dissolved cornstarch and stir in. As soon as the poppy seed filling has thickened, stir in the egg. Let the filling cook for a moment, then remove from the heat. Place a piece of plastic wrap directly on the surface of the poppy seed filling and let it cool down completely.

3. For the streusels, mix the flour, sugar, ground cinnamon, and salt in a bowl. Add the butter and vanilla extract and rub everything between your fingers to create different-sized streusels. Place the bowl in the fridge until ready to use.

4. Roll out the dough on a well-floured work surface into a rectangle of about 30x40cm (12×16 inches) – the dough will be quite soft and sticky. Spread the poppy seed mixture evenly on top of the dough. Leave about two finger-widths free on one of the longer sides. Brush this area with a little egg white and then roll up the dough tightly from the opposite side.

5. Position the dough roll on the work surface with the seam side facing down. Cut the roll in half lengthways and intertwine the two resulting strands. This works best if you first only cut halfway through the roll and intertwine the two strands, then turn everything over and repeat the procedure on the other side. Place the braided dough strands on a baking tray lined with baking parchment, cover and let rise another 10 minutes.

6. Preheat the oven to 200°C (390°F). Brush the dough with the remaining egg white, sprinkle the streusels on top and press them down lightly. Bake the Mohnstriezel in the center of the oven for about 28-30 minutes or until the streusels got some color. Take out of the oven and pull the Monstriezel with the baking parchment onto a cooling rack. Let cool down completely, then decorate with sugar icing, if desired (optional).