Onion Soup - Borges India

Ingredients

• 180 g unsalted butter
• 2 tablespoons Borges extra virgin olive oil
• 3 medium onions
• 1.2 liters of beef broth
• 2 tablespoons balsamic vinegar of Modena
• 1 teaspoon dried thyme
• Salt and pepper
• 4 slices of bread
• 4 slices of provolone cheese
• 2 slices of Swiss cheese
• 80 g grated Parmesan cheese