Soak the diced bread in milk. In the meantime wash and clean the salad and drain well. Peel and finely dice onions.
Wash, peel and coarsely rub the beetroot (Attention, wear disposable gloves - strong staining!). Fry the grated beetroot and half of the onion cubes in 2 tablespoons of hot butter. Chop parsley. Knead beetroot mix, parsley, eggs and flour with the bread and season. Form into about 12 small dumplings and cook in boiling salted water for about 10 minutes.
Wash, dry, quarter and core the apples. Cut quarters into slices. Fry the bacon in a pan without fat until crispy and remove. Fry apples briefly in hot bacon fat. For the vinaigrette, mix vinegar, salt, pepper and sugar. Fold in the oil. Peel, wash and finely grate the horseradish.
Lift out the dumplings and let them drain. Mix the salad with the rest of the onion, apples and the vinaigrette. Heat 1 tablespoon butter in a frying pan and toss the dumplings briefly in it. Arrange on the salad. Crumble the bacon and sprinkle with horseradish.