Knead the flour, baking powder, sugar, salt, cardamom, eggs and butter into a dough and chill for at least 2 hours. Meanwhile, boil down the plum jam with rum until thick.
Roll out the cooled dough and cut out circles. Put 1/2 teaspoon of plum jam on each circle and fold over to semi-fashions. Press the ends lightly with a fork. Brush each cookie with milk and bake in a preheated oven at 160 - 180 ° C.
After cooling, dust half of the cookies with cocoa and the other half with powdered sugar.