Onion gravy is a brown sauce made by cooking sliced onions in the fat and drippings left in a pan after roasting meat, then thickening the mixture with a flour-based roux and stock or broth. Common in British and Irish cooking, it developed as a way to use pan drippings and cheap, plentiful onions to stretch a meal, and it remains a staple with bangers and mash, roasted meats, and other pub fare. The onions are cooked slowly until soft and caramelized for sweetness before the roux and stock are added and simmered until the gravy thickens to a smooth, clinging consistency; seasonings like Worcestershire sauce, thyme, and black pepper round out the flavor. Onion gravy differs from a pan jus, which is unthickened meat drippings simply deglazed with liquid, and from a plain roux-based gravy without the caramelized-onion base. Some regional versions add ale or stout for extra depth.