French Onion Soup (Soupe à l'Oignon Gratinée) Recipe | Dinner | Umami

Ingredients

• 6 tablespoons (90g) unsalted butter, plus more for bread
• 3 pounds (1.4kg) yellow or mixed onions, sliced 1/8 inch thick (see note)
• Kosher salt and freshly ground black pepper
• 1/2 cup (120ml) dry sherry (such as Amontillado)
• 2 quarts (1.8L) homemade or store-bought low-sodium chicken stock
• 2 sprigs thyme
• 1 bay leaf
• 1 teaspoon (5ml) Asian fish sauce (optional)
• 1 teaspoon (5ml) cider vinegar
• 8 bowl-size slices rustic bread, toasted until crisp
• 1 medium clove garlic
• 1 pound (450g) Gruyère cheese, grated
• Freshly minced chives, for garnish