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1
Melt butter in large Dutch oven over medium heat.
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2
Stir in the onions and 1 teaspoons salt, cover, and cook until the onions are wet and slightly wilted, about 10 minutes.
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3
Uncover and continue to cook, stirring occasionally, until the liquid cooks off and onions are translucent, about 20 minutes.
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4
Reduce the heat to low and continue to cook the onions, frequently scraping up any browned bits on the bottom of the pot, until deep brown and very soft, 40 to 60 minutes.
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5
Continue to cook onions, stirring every 5 minutes, until a dark crust covers the bottom of the pot, about 10 minutes.
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6
Stir in 1/4 cup water, scrape up the crust, and continue to cook until another dark crust forms, 2 to 3 minutes; repeat this process 2 more times.
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7
Stir in the chicken broth, remaining 4 cups water, thyme, and bay leaf, scraping up any final bits of the browned crust.
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8
Bring to a simmer and cook for 10 minutes.
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9
Remove and discard the thyme and bay leaf.
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10
Turn off the heat, stir in the sherry and season with salt and pepper to taste.
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11
Meanwhile, adjust an oven rack to the middle position and heat the oven to 325F
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12
Arrange the baguette slices in a single layer on a baking sheet and bake until the bread is dry, crisp, and very slightly colored at the edges, about 10 minutes; set aside.
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13
TO SERVE:.
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14
Adjust an oven rack 6 inches from the broiler element and heat the broiler.Set individual broiler-safe soup bowls or crocks on a baking sheet and fill each with about 1 3/4 cups of soup.
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15
Top each bowl with 2 baguette slices and sprinkle evenly with the cheese.
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16
Broil until browned and bubbly, 5 to 10 minutes.
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17
Cool 5 minutes before serving.
