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1
Heat a large Dutch oven over medium heat.
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2
Add 6 tablespoons of the butter and let it melt.
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3
Stir in the onions and the thyme and season with salt and pepper, to taste.
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4
Cook, stirring occasionally, until the onions caramelize, about 40 to 45 minutes.
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5
Meanwhile, put the mushrooms in a small pot and cover with a couple of cups of water.
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6
Bring to a boil over high heat, then reduce the heat to low and simmer to reconstitute the mushrooms.
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7
Add the sherry to the pot with the onions, to deglaze the pan, then stir in the wine.
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8
Remove the mushrooms from their broth with a slotted spoon to a cutting board.
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9
Chop them, and add them to the onions.
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10
Add all but the last 1/2 cup of the mushroom liquid to the soup, about 1 cup.
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11
Add herb bundle and the beef stock to the pot and simmer the soup for 30 to 45 minutes.
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12
Cool and refrigerate for a make-ahead meal.
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13
Reheat over medium heat, covered, and prepare the croutons when ready to serve.
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14
Heat the oven to 425 degrees F. Toast the bread on a rack over a baking sheet, until deep golden brown.
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15
Butter the bread, using the 2 tablespoons of remaining butter and liberally rub them with the cut garlic.
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16
Top the toasts with the cheeses and return them to the oven until the cheese is melted and bubbly.
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17
Toasts may be arranged on top of crocks of soup, put on baking sheet, then topped with cheese and baked to brown, for a more dramatic presentation.
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18
Ladle the soup into serving bowls and serve with the cheese toasts.
