In a large skillet, cook pork sausage until browned, breaking it apart as it cooks. Add onion and cook a minute longer. Pour off excess fat. Stir in butter. Reduce heat and quickly stir in flour. Slowly add milk, stirring constantly. Cook until gravy is thickened. Stir in additional milk if a thinner gravy is desired. Add spices. Serve over hot biscuits.