– 3 large onions, halved and sliced – 3 tablespoons butter (or 2 tablespoons butter + 1 tablespoon olive oil) – ½ teaspoon salt, divided – ½ teaspoon pepper, divided – 64 ounces beef broth – 1 garlic clove, minced – 1 tablespoon Worcestershire sauce – 1 tablespoon balsamic vinegar – 1 bay leaf – ½ teaspoon dried thyme – 6 slices French bread – 1 cup grated Gruyère cheese
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Continue cooking on low for 6–8 hours.Ladle soup into broiler-safe dishes or ramekins.
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