"This delicious soup turns any meal into a festive occasion. Cook the onions low and low for a sweet, irresistible flavor, then add aged Gruyère for the perfect, bubbly topping...."
INGREDIENTS
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2 oz. (1/4 cup) unsalted butter, plus more for the baking sheet
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4 medium-large yellow onions (about 2 lb.), thinly sliced (8 cups)
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Kosher salt
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Freshly ground black pepper
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1 tsp. granulated sugar
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1 small baguette (1/2 lb.), cut into 1/2-inch slices
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2 quarts canned beef or chicken broth
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1 bay leaf
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2 cups grated Gruyère