Remove any fat from the meat and cut into thin strips about 2-inches long. Sprinkle with freshly ground pepper and let stand in cool place for 2 hours in heavy skillet (cast iron if possible). Saute mushrooms until tender; remove from skillet. Saute onion in same pan until transparent. Brown meat on all sides and remove from skillet. Add flour to oil in skillet; add broth and stir until thick. Add tomato paste, mustard, oregano, dill weed and wine. Blend well. Combine sauce with meat and all ingredients in top of double boiler. Cook for 20 minutes. Beat yogurt to prevent curdling. Blend in beaten yogurt 5 minutes before serving. Serves 6.