Instructions

1. In a heavy, wide-bottomed saucepot, add the butter over medium-low heat. Once it begins to foam and sizzle, add the onions and garlic.
2. Cook, stirring occasionally until the onions begin to get very soft and release their juices, about 20 minutes. Add 1 teaspoon of the salt, the pepper, bay leaves, and 1 tablespoon of the thyme and continue to cook, stirring occasionally, until the onions are fully caramelized and deep golden brown, about 40 more minutes.
3. Meanwhile, toast the baguette slices. Preheat the oven to 350°F.
4. Arrange the baguette slices in a single layer on a baking sheet and drizzle both sides with the olive oil. Bake, flipping once halfway through, until golden-brown and toasted, about 10-12 minutes.
5. Discard the bay leaves and stir in the tomato paste and the flour. Turn the heat to medium and cook, stirring occasionally, for 2 minutes. Deglaze the pan, scraping up any bits from the bottom, with the Worcestershire, sherry, wine, and beef broth. Bring the soup to a boil and stir constantly until lightened thickened, about 2-3 minutes, and then add the remaining 1 teaspoon of salt.
6. In a 9x13-inch baking dish, layer half of the toasted baguette slices and spoon the onion soup over top. Evenly top with the remaining baguette slices and cheese. Cover the dish with foil and bake for 30 minutes.
7. Remove the foil and broil the casserole until the cheese is bubbly and lightly golden. Divide among bowls and top with the remaining 1 tablespoon of thyme.