In a large, heavy-bottomed saucepan, combine all ingredients, cover, and bring to a boil. Reduce to a simmer and cook 40 minutes, shaking the pan occasionally so that the onions don't stick to the bottom of the pan. The onions should be easily penetrated with a paring knife but should not be falling apart.
Remove the lid and continue to cook until the liquid has evaporated and the onions are glossy and dark brown, taking care not to burn. Remove from heat and serve.