Brown the meat slowly in a 3 quart casserole with oil and butter. Mix anchovies, garlic, fennel, lemon peel and vinegar. When meat is well browned, add salt and pepper and the anchovy mixture. Mix well and cook until vinegar has evaporated almost entirely. Sprinkle flour over the meat and stir well. Add stock. Cook for 30 minutes longer, stirring frequently. Serves 4