French Onion Soup Recipe Without Wine

Ingredients

• 2 tablespoons olive oil
• 2 tablespoons unsalted butter
• 3 pounds yellow onions (thinly sliced)
• 1 teaspoon salt
• ½ teaspoon black pepper
• 3 tablespoons all purpose flour
• 1 tablespoon fresh thyme leaves (or ½ teaspoon dried thyme)
• 8 cups beef broth
• 2 tablespoons red wine vinegar
• 8 slices French bread
• 1 ½ cup freshly grated Gruyere (divided)