While you wait for the yeast dough to rise for the first time, cut the prunes into small pieces. Brush the ring cake mould with melted butter and then sprinkle it with the cinnamon sugar. (The baking process will turn this sugar into a tasty caramel.)
On a floured working surface, roll out the risen yeast dough to form squares 7 mm thick. Brush the yeast dough with melted butter and sprinkle it with a bit of the cinnamon-sugar. Distribute the marinated prunes evenly on top and then roll up the dough squares. Place these rolls in the ring mould, making sure that their ends touch with no gaps in between. Let the ring rise once more, for 40 to 45 minutes. Afterwards, brush the exposed top side of the dough with melted butter and sprinkle with a bit of cinnamon-sugar. Bake the ring cake in the oven at 170 °C for ca. 60 minutes.