Dice the lean beef and put it into a saucepan with 2 quarts of salted water. Bring the water slowly to a boil; skim carefully, and add parsley, leek, and carrot. Add bay leaf, garlic, and peppercorns. Simmer, covered, for 1 1/2 hours, skimming from time to time. Remove the meat from the soup; strain soup into a saucepan and add beets, red cabbage, potato, onion, and mushrooms. Bring to a boil, skim, and simmer uncovered, for 1 1/2 hours. Return meat. Chill and stir in sour cream before serving.
