1 cup (2 sticks) unsalted butter
8 onions, sliced
4 garlic cloves, chopped
4 bay leaves
4 fresh thyme sprigs
3 tablespoons tomato paste
1 ounce sherry vinegar
Kosher salt and freshly ground black pepper
1/4 cup flour
2 cups red wine
2 quarts beef stock
2 quarts chicken stock
1 baguette, cut on long bias into 20 slices
4 ounces melted butter
10 slices Gruyere
10 sage leaves
To make soup, melt the butter in a large pot over medium heat. Add the onions, garlic, bay, thyme, tomato paste, sherry vinegar, and salt and pepper to taste. Cook until the onions are very soft and caramelized, about 25 minutes.
Add the wine, bring to a boil, then lower the heat and simmer until the wine has evaporated and the onions are dry, about 5 minutes. Discard the bay leaves and thyme sprigs.
Dust the onions with the flour, then give them a stir. Turn the heat down to medium-low and cook, stirring occasionally, for 10 minutes, being careful not to burn the flour.
Add the two broths, bring the soup back to a simmer, and cook for 10 minutes. Season to taste, with salt and pepper.
To make the sandwiches, coat the baguette slices with butter. Place a slice of Gruyere and a sage leaf between two slices of bread to form each sandwich. Griddle on both sides. Place in soup to serve.
– Barbara Llewellyn Catering & Event Planning