Homemade French Onion Soup

Ingredients

• 4 large yellow onions, thinly sliced
• 4 tablespoons unsalted butter
• 1 tablespoon olive oil
• 1 teaspoon sugar (optional)
• 4 cups beef broth (or vegetable broth for vegetarian)
• 1 cup dry white wine (optional)
• 2 teaspoons fresh thyme leaves or 1 teaspoon dried thyme
• 1 bay leaf
• Salt, to taste
• Freshly ground black pepper, to taste
• 4 slices of French baguette, toasted
• 1 ½ cups grated Gruyère cheese