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1
Preheat the oven to 400F
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2
Generously grease the inside of a large Dutch oven with nonstick cooking spray.
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3
Place the butter into the Dutch oven, then add the onions with 1 teaspoon salt.
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4
Cook covered for 1 hour, then remove from the oven and stir onions, making sure to scrape the bottom and sides of the pot.
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5
Return the pot to the oven with the lid slightly ajar and continue to cook until the onions are very soft and golden brown (about 1 1/2 hours). Make sure to stir the onions and scrape the sides of the pot after 1 hour.
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6
Remove the pot from the oven and place over medium-high heat.
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7
Cook the onions, stirring frequently and scraping the sides of the pot until the liquid evaporates and the onions brown (use oven mitts to handle the pot), or for about 15 to 20 minutes.
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8
Continue to cook, stirring frequently, until the bottom of the pot is coated with a dark crust (another 6 or 7 minutes).
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9
Once the onions are a very dark brown, add the garlic and continue to stir for another 30 seconds to a minute, or until the garlic becomes fragrant.
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10
Stir in the sherry and red wine, and cook, stirring frequently until the liquid evaporates (another 7 to 10 minutes).
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11
Stir in the broths, 2 cups water, thyme, bay leaf, and 1/2 teaspoon salt, making sure to scrape the bottom of the pot as you do to loosen everything up.
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12
Increase the heat to high until simmering, then reduce the head to low, cover, and cook for 30 minutes.
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13
Meanwhile, arrange baguette slices on a baking sheet and bake about 10 minutes in the oven.
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14
Remove and discard the herbs from the soup, then season with salt and pepper to taste.
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15
To serve, adjust oven to boiling.
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16
Ladle soup into the bowls, then top with 1 or 2 baguette slices. Sprinkle with Gruyere cheese, then broil until the cheese is melted and bubbly around the edges (3 to 5 minutes).
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17
Let cool 5 minutes before serving.
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18
Enjoy!
