1. Sift the flour for the dough into a large bowl. Make a small depression in the center and crumble the yeast into it. Add a bit of sugar to the yeast and mix with a bit of the lukewarm milk to create a pre-dough. Cover the bowl and let rise in a warm place for about 10-15 minutes.

2. For the streusels, mix flour, sugar, salt, and ground cinnamon in a bowl. Add the cold butter in small pieces. Rub everything between your fingers to get different-sized streusels. Place the streusels in the fridge until needed.

3. Add the remaining milk, sugar, butter, egg, and a pinch of salt to the bowl with the flour and pre-dough and mix everything and knead until you get a smooth dough. Cover the bowl and let the dough rise for about 30 minutes.

4. Preheat the oven to 200°C (390°F). While the dough rises, wash, dry, pit, and quarter the plums lengthwise. Line a baking sheet or two round baking tins (Ø10 inches) with baking parchment. Roll out the dough and place it on the baking sheet or in the baking tins, forming a small border along the edges. Place the plums tightly next to each other on the dough and distribute the streusels evenly on top. Bake the cake(s) for about 28-30 minutes until the streusels got some color – the edges should not get too dark though. Remove the cake(s) from the oven and let cool down on a wire rack.