French Onion Soup Burger Recipe - (4.5/5)

Ingredients

• 5 tablespoons butter, plus more for buttering muffins
• 1/3 cup cognac
• 4 large Spanish onions, halved lengthwise and cut into thin half-moon slices
• 2 sprigs fresh thyme
• 1 cup beef or chicken stock
• 2 tablespoons flour
• 1 1/4 cups milk, warmed
• 20 ounces (1 1/4 pounds) grated Emmental cheese
• Salt and freshly ground white pepper
• 3 pounds ground beef, a mixture of 70 percent chuck and 30 percent brisket, chilled
• Olive oil, for brushing
• Light brown sugar, for sprinkling
• 6 large English muffins, such as Thomas', toasted
• Dijon mustard, for topping