Dredge pot-roast in flour; brown all sides in cooking oil in Dutch oven. Slip rack under meat; sprinkle with salt and pepper. Add water, garlic, onion, tomato sauce, bay leaf and thyme. Cover and cook in slow oven (325 degrees F.) 3.5 hours or until tender. Cook sliced mushrooms in butter in small frying-pan until tender and golden. When meat is tender, remove to cutting board. Remove bay leaf. Thicken cooking liquid with 2 T flour combined with quarter c water, if desired. Add mushrooms and sour cream to cooking liquid; cook over moderate heat but do not allow to boil. Slice beef; serve with hot buttered noodles sprinkled with paprika. Pass our cream sauce separately.