For the plum gingerbread, heat honey with sugar in a saucepan. Pour into a mixing bowl and add milk, dissolved staghorn salt, flour, yolks, egg and gingerbread spice. Mix briefly and add dissolved potash and knead. Let rest for 1 to 2 days.
Roll out the gingerbread dough to a thickness of at least 5 mm. Using a round cookie cutter, cut out circles about 4 cm in size. Place on a prepared baking sheet and bake in a preheated oven at 165 °C for about 10 minutes until light brown. (You may want to bake a sample beforehand. If the dough is too soft, knead in some more flour).
For the filling, grind dried plums in the Moulinette or mince with the attachment of the food processor. Mix with rum and jam and place small heaps on the gingerbread cookies while they are still warm. Allow to cool.
For the glaze, melt couverture over a water bath or in the microwave and stir with coconut oil until smooth. Dip the plum gingerbread cookies upside down in it until they reach the edge of the cake, let them drip off and place them on a baking mat or on baking paper and let them dry.