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1
Melt butter in a large soup pot over medium heat.
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2
Cook and stir onions, garlic, salt, black pepper, and thyme until onions are soft and brown, about 30 minutes.
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3
Pour in red wine and sherry; bring to a boil.
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4
Reduce heat to low and simmer until you can no longer smell alcohol cooking off, about 15 more minutes.
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5
Sprinkle onion mixture with flour and stir until coated; cook for 10 minutes.
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6
Pour in broth, stir to blend in flour, and simmer until slightly thickened, about 20 minutes.
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7
Preheat oven to 350 degrees F (175 degrees C) while soup is simmering.
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8
Arrange bread slices on a baking sheet and drizzle with olive oil.
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9
Toast the baguette slices in the preheated oven until golden brown, 12 to 14 minutes, turning the bread over halfway through cooking.
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10
Remove toast and set aside.
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11
Set an oven rack about 8 inches from the heat source and turn on the oven's broiler.
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12
Ladle soup into 6 oven-proof crocks, filling them about 3/4 full.
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13
Place 1 or 2 bread slices into the bowls and top each with a slice of Swiss cheese and a slice of provolone.
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14
Carefully place filled crocks onto a sturdy baking sheet.
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15
Broil soup until the cheese is browned and bubbling, 3 to 4 minutes.
