2 tbsp olive oil
6 yellow onions, sliced
¼ tsp black pepper
½ dry red wine
¼ cup sherry
4 cups unsalted chicken broth
2 cups unsalted beef broth
2 thyme twigs
1 bay leaf
6 leaves parsley
In a Dutch oven or large saucepan, heat olive oil over medium-low heat. Add the sliced onions and cook, stirring occasionally, until soft and deeply golden about 30 minutes.
Add the wine, chicken broth, beef broth, pepper, thyme, parsley, and bay leaf. Bring to a gentle simmer and cook for 30 minutes to develop flavor.
Stir in the sherry and continue to simmer for an additional 30 minutes. Remove the bay leaf, thyme, and parsley before serving.
Ladle into bowls and serve as is, or top each bowl with a toasted baguette slice and a slice of Gruyère cheese.
If adding bread and cheese, place oven-safe bowls under a broiler at 450°F until the cheese is melted and golden brown.