Easy French Onion Soup

Bahan-bahan (4 porsi)

• 3 tablespoons butter
• 1/2 tablespoon olive oil
• 2 pounds (about 3) yellow onions, (thinly sliced)
• 1/2 teaspoon granulated white sugar
• 1/4 teaspoon salt
• 1/8 teaspoon pepper
• 2 tablespoons all purpose flour
• 6 cups beef broth
• 1 whole bay leaf
• 8 slices baguette
• 4 ounces (1 cup) grated Gruyere cheese
• 1 ounce (1/4 cup) freshly grated Parmesan cheese
• fresh thyme for garnish, (optional)