French Onion Soup

Ingredients

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

Directions

1. Melt the butter over medium-high heat in a large stainless steel saucepan, or use 2 large stainless steel or cast iron skillets, and let it foam. Stir in the onions and cook, mixing now and then, until they begin to soften, about 8 minutes. Turn the heat down to medium-low and continue cooking, stirring often, until the onions are deeply golden-brown and very sweet, 1 to 2 hours. If the browned bits on the bottom look like they may scorch, pour in 1 tablespoon (15ml) water, scrape the pan well, and keep going. Add salt and pepper to taste.
2. Pour in the sherry and let it come to a simmer, scraping the bottom to loosen any browned bits. If you used 2 skillets, split the sherry between them, then transfer the onions and liquid from both pans into a pot or Dutch oven before continuing. Cook until the sharp alcohol aroma has mostly cooked off, about 3 minutes. Add the stock, thyme, and bay leaf, then increase the heat to medium-high and bring everything to a simmer. Reduce the heat and simmer for 20 minutes.
3. Stir in the fish sauce, if using, along with the cider vinegar. Taste and adjust with salt and pepper. Remove and discard the thyme sprigs and bay leaf.
4. Heat the broiler and move the oven rack to the top position. Butter the toasts, then rub them with the garlic clove until they smell fragrant. Ladle a little broth into the bottom of 4 ovenproof serving bowls, then add half the toasts. Scatter some grated cheese over the toasts, then ladle in more soup and onions until the bowls are nearly full. Place the remaining 4 toasts in the bowls, pressing them down until they are almost submerged. Cover with the remaining grated cheese and place the bowls on a rimmed baking sheet. Broil until the cheese has melted and browned in spots. Finish with chives and serve.