The potatoes are peeled, washed and cut into small pieces. These are then steamed for 10-15 minutes so that they are 3/4 through.
The mushrooms and onions are cut into small pieces and fried in a pan with olive oil. Fry the mushrooms shorter than the onions; if necessary fry separately and then deglaze the mushrooms with a little red wine.
Mash the steamed potatoes with the onions and mushrooms in a bowl and season. Shape the potato mixture into potato-sized balls and coat with bacon. Place the rosemary sprigs on the bacon and tie the roast with cooking threads or something else. Bake the balls in an oven preheated to 180 ° C for 20-25 minutes.
Boil the red wine in a pan. Add soy sauce until it boils and then sake until it boils. Then add the butter. Stir the butter while it melts.