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1
In a large soup pot or Dutch oven, melt the butter over medium heat.
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2
Add the onions, stir to combine with the butter, cover, and cook for 30 minutes, stirring occasionally.
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3
Remove the cover; increase the heat to medium-high and cook, until the onions are brown and caramelized, about 30 minutes.
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4
(Stir the onions frequently toward the end of this stage in the cooking, so they do not scorch or burn.)
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5
Add the thyme and garlic, saute for 2 to 3 minutes more.
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6
Pour in the wine and scrape up the browned bits from the bottom of the pan with a wooden spoon; simmer until the wine is reduced by about half.
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7
Stir in the broth and salt and bring to a gentle simmer.
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8
Cover, and cook for 30 minutes.
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9
Add the Cognac, if using, and season with pepper to taste.
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10
(The soup can be made to this point a day ahead and refrigerated.)
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11
When ready to serve pre-heat the broiler.
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12
Heat the soup and divide it evenly among 6 heatproof crocks or bowls.
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13
Top each soup with a slice of the bread and about 1/2 cup of the cheese.
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14
Place the bowls on a sheet pan and broil until the cheese is bubbly and brown.
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15
Carefully transfer each crock to an under-lining plate.
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16
Serve immediately.
