Mix the butter, sugar and salt until foamy, cut the marzipan into small pieces, add to the butter and stir everything until smooth.
Add the eggs, milk and rum flavor. Pass the flour with the baking powder through a sieve and gradually stir in.
Put the dough in a greased springform pan and stick the prepared plums close together in the dough. Bake in a preheated oven at 175 degrees for 60-70 minutes.
If necessary, after 40 minutes of baking, cover the cake with a sheet of baking paper so that it does not get too dark.
After baking, let the cake cool down and sieve over it with powdered sugar.