INGREDIENTS
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2 tablespoons butter
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4 yellow onions (about 1 3/4 pounds), thinly sliced with the grain to hold their shape
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Kosher salt and freshly ground black pepper
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1 teaspoon flour
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1/2 cup dry red wine
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1 tablespoon chopped fresh thyme
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1 bay leaf
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1 teaspoon lemon juice
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2 cups beef stock
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2 cups chicken stock
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1/2 cup grated Swiss
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1 tablespoon grated Parmesan
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4 (1-inch thick) baguette slices, cut on the bias