1. Preheat the oven to 375°F (190°C). Line a small baking sheet (about 12×10 inches) with baking parchment and grease lightly. Set aside. Wash, dry, half, and pit the Damson plums for the topping. Then cut the halved plums in half again lengthwise. Set aside as well.

2. Mix the spelt flour, sugar, and cinnamon for the streusels in a bowl. Add the butter and mix until you get different-sized streusels. Place them in the fridge until ready to use.

3. Mix the yogurt for the dough with the oil, egg, vanilla extract, and sugar in a large bowl. Combine the spelt flour, baking powder, and salt and add to the bowl – mix/knead until you get a smooth dough. Roll it out on a lightly floured surface, place on the baking sheet, and press it to the bottom and into the corners. If the dough is tough to work with and does not want to stretch, let it rest for a moment and then try again.

4. Place the Damson plum slices close to each other on top of the dough. Mix the plum jam with sugar and water in a small bowl and brush the plums with it. Sprinkle the streusels all over the plums and bake the cake in the preheated oven for about 28-30 minutes. Remove the cake from the oven and let it cool down completely. Serve with some whipped cream.