Peel and finely dice the onions. Clean, wash, drain well and cut into slices. Peel, wash and finely dice the potatoes.
Heat the oil in a large pan, fry the mushrooms to a tablespoon, turning them over. Add the onions, marjoram and potatoes and fry briefly. Season with salt and pepper. Deglaze with stock, bring to the boil and simmer covered for about 18 minutes.
In the meantime, wrap each plum tightly with a strip of bacon. Heat a pan without fat. Fry the bacon plums in it until crispy, turning them over. Take out, let it cool down a bit, put 2 bacon plums on 1 skewer.
Add the rest of the mushrooms to the pan and fry them while turning. Season with salt and pepper and remove.
Remove the mushroom soup from the stove, puree finely. Add cream, bring to the boil again, season to taste with salt and pepper. Fill soup into bowls, garnish with fried mushrooms and marjoram leaves, place skewers on top.