Cut the cleaned mushrooms into wedges. Also cut shallots lengthwise into wedges and sauté in hot vegetable oil. Add mushrooms and brown lightly. Add bacon strips and fry briefly. Season with salt and pepper and keep warm.
Cut the cleanly trimmed calf’s liver (without skin and veins) into flakes and fry briefly in hot oil in a coated pan, swirling constantly, but do not fry through (otherwise the liver will become hard). Add finely chopped shallots, roast briefly and transfer liver to a plate.
Deglaze the roast residue with vinegar, add stock and boil down vigorously.
Add liver again, salt, pepper and bind with cold butter while swirling vigorously. (If necessary, knead a little additional flour with the butter, stir in and thicken the sauce with it). Serve on warmed plates, sprinkle with the mushroom-bacon mixture and garnish with plucked marjoram.