Preheat oven to 315 degrees. Brush 6 cup capacity casserole with butter. Melt butter in frying pan. Coat meat with flour. Saute meat until brown. Remove and place in casserole dish. Add onions, celery, and parsnip to the pan. Saute until parsnip is cooked, spoon over meat. Sprinkle remaining flour in saute pan and cook until dark brown in color. Gradually pour in stock and stir until the mixture comes to a boil. Add mushrooms, pepper, salt, herbs and worcestershire sauce, simmer for 10 minutes. Remove and pour over meat. Place overlapping potato slices over meat and vegetables. Cover casserole with lid and cook for 1 hour. Remove lid and cook until potatoes turn brown.