Here’s how to prepare it:
Place the flour in a bowl and make a well in the bowl. Heat the milk to lukewarm. Crumble the yeast into the well, mix with 50 ml of milk, 1 teaspoon of sugar, and a little flour from the sides. Cover and let rise in a warm place for about 15 minutes.
Add the remaining milk, 65g sugar, 60g butter, the egg, a large pinch of salt, and coriander to the pre-dough. Knead first with a dough hook, then with your hands until a smooth dough forms. Cover and let rise for about 45 minutes until doubled in size.
Meanwhile, use a knife to cut a cross-shaped incision along the top and bottom of the plums, then cut open along one long side. Stone the plums and lightly cut the inside of the cross-shaped incisions so that the plums fan out.
Preheat oven to 200°C (180°C fan-assisted oven). Butter the baking sheet. Briefly knead the dough, roll it out on a lightly floured surface to the size of the baking sheet, and place it on the baking sheet. Spread with jam (preferably homemade; see recipe!) and top with plums in a shingle-like pattern. Mix the cinnamon with 1 tablespoon of sugar and sprinkle over the plums. Sprinkle the remaining butter on top. Bake on the lowest rack for about 30 minutes.
