Let the meat stand at room temperature for 1 1/2-2 hours. Stir fry the onion, carrot and celery in butter over low heat until tender but not brown (about 10 minutes). Mix in the grated lemon rind. Preheat the oven to 450 degrees. Spread the vegetable mixture over the meat. Lay the bacon slices over the top. Insert a meat thermometer in the center. Roast, uncovered, on a rack in a shallow roasting pan for 5-6 minutes per pound for rare (120 degrees-125 degrees) to 7-8 minutes per pound for medium rare (130 degrees-140 degrees). Remove and discard the bacon and vegetables. Transfer the meat to a steak board. Keep warm. Skim the fat from the drippings. Smooth in the sour cream. Warm gently, but Do Not Boil, for 1-2 minutes. Garnish the beef with stuffed mushroom caps and parsley. Top with some of the sauce. Sprinkle with paprika. Serve the remaining sauce in a gravy boat.