Sieve the flour into a bowl, make a well, crumble in the yeast, mix with the sugar and milk. Cover and let rise until the batter has doubled.
Add egg, butter, salt and vanilla sugar and knead into a smooth dough. Cover and let rise for 30 minutes.
Stone the plums. Roll out the dough 2 cm thick, cut into 8 cm squares, cover each with 2-3 plums and sprinkle with sugar. Fold it up and brush with butter.
Put in a greased springform pan, let rise for 30 minutes and bake in a hot oven at 190 ° C for about 25 minutes.