Rarebit sauce is traditionally served on a thick slice of toast. Spread the rarebit on the toast and put it under the salamander or broiler until the sauce is hot and bubbly. Serve as toast, or as an open-faced sandwich with bacon, red onion, and tomato. To use on top of a burger, heat the rarebit sauce and ladle over the burger patty and any accompanying ingredients. To use as a cheese sauce for fries, heat and ladle over fries. We recommend adding diced tomato, minced red onion, and bacon lardons.