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 1/2 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 1/4 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.