- 2 tablespoons butter
- 4 yellow onions (about 1 3/4 pounds), thinly sliced with the grain to hold their shape
- Kosher salt and freshly ground black pepper
- 1 teaspoon flour
- 1/2 cup dry red wine
- 1 tablespoon chopped fresh thyme
- 1 bay leaf
- 1 teaspoon lemon juice
- 2 cups beef stock
- 2 cups chicken stock
- 1/2 cup grated Swiss
- 1 tablespoon grated Parmesan
- 4 (1-inch thick) baguette slices, cut on the bias
In a heavy bottomed Dutch oven or large saucepan, melt the butter over medium-low heat. Add the onions, sprinkle with salt, cover, and cook until deeply caramelized, 1 to 1 1/2 hours. Turn the heat up to medium and sprinkle the onions with the flour. Stir and allow to cook for 1 or 2 minutes. Deglaze the pan with the red wine. Add the thyme, bay leaf, lemon juice, and stock and simmer for 10 minutes. Taste and add salt and pepper, as needed. Ladle the soup into 4 ovenproof crocks.
Heat the broiler to high. Mix the cheeses together in a small bowl. Top each crock with a baguette slice and evenly distribute the cheese on top of each. Place the crocks under the broiler just until the cheese is bubbly and browning, about 1 minute. Serve hot.