Combine Combine the onion, chili sauce, vinegar, ketchup, beef consommé, hot sauce, Worcestershire sauce, and brown sugar in a heavy-bottomed, nonreactive saucepan.
Bring to a simmer Place the pan over medium heat and stir until the brown sugar dissolves and the mixture reaches a gentle simmer.
Cook slowly Reduce the heat to low. Cook at a slow, steady simmer for 2–3 hours, stirring occasionally and scraping the bottom and sides of the pan.
Finish As the sauce reduces, stir more frequently to prevent scorching. It is ready when the onion is very tender, the flavors have blended, and the sauce lightly coats a spoon. The sauce will thicken further as it cools.
Use or store Use warm, or cool promptly and refrigerate in a covered container.