The Best French Onion Soup - Andrew Zimmern

Ingredients

• 2 tablespoons extra-virgin olive oil
• 2 large onions, halved and thinly sliced (7 cups)
• 2 leeks, whites and light green parts only, thinly sliced
• 1 cup thinly sliced shallots (2 large)
• Kosher salt
• 5 garlic cloves, minced
• 3 tablespoons tomato paste
• 1 tablespoon herbs de Provence
• 1 bay leaf
• 1 cup dry red wine
• 1/4 cup sherry vinegar
• 8 cups beef stock or low-sodium broth
• Freshly ground pepper
• 1 stick unsalted butter, cut into chunks
• 12 baguette slices, cut 1/2 inch thick
• 4 ounces Gruyère cheese, shredded (1 cup)
• Finely chopped thyme, for garnish