Ooh La La! My Secret French Onion Soup Recipe

Ingredients

• 3 pounds yellow onions, thinly sliced (about 1.36 kg)
• 4 tablespoons unsalted butter (57g)
• 2 tablespoons olive oil (30 ml)
• 1 teaspoon granulated sugar (5g)
• 1/2 teaspoon kosher salt (3g)
• 1/4 teaspoon freshly ground black pepper (1g)
• 1/4 teaspoon dried thyme (1g)
• 8 cups beef broth, low sodium (approximately 1.9 liters)
• 1 cup dry red wine (like Cabernet Sauvignon or Merlot) (approximately 240 ml) Optional
• 2 tablespoons all-purpose flour (15g) Optional, for thickening
• 2 bay leaves
• 1 tablespoon balsamic vinegar (15 ml)
• 1 baguette, sliced into 1-inch thick rounds
• 6 ounces Gruyère cheese, grated (about 170g)