French Onion Soup

Ingredients

• 3 tablespoons unsalted butter
• 2 1/2 pounds yellow onions, halved and sliced 1/8 inch thick
• 1/2 teaspoon fine sea salt
• 1 cup water, divided, as needed during onion caramelization
• 2 garlic cloves, minced
• 1 tablespoon all-purpose flour
• 6 cups flavorful low-sodium beef stock or chicken stock
• 1 teaspoon dried thyme
• 1 bay leaf
• 1/4 teaspoon black pepper
• 8 baguette slices, 1/2 inch thick (about 4 ounces)
• 4 ounces Gruyère cheese, grated (about 1 cup)
• 2 teaspoons apple cider vinegar

Method

1. 1

   Step 1. Allow roughly 2–3 hours: 15 minutes preparation, 60–120 minutes caramelizing onions, then about 25–30 minutes heating and simmering the soup. A typical batch takes about 2 1/2 hours. Use a wide heavy 6-quart pot, a broiler-safe metal sheet pan and four large soup bowls. The cheese toasts cook separately while the soup simmers.

2. 2

   Step 2. Melt the butter over medium heat. Add the onions and salt; turn often for 10–15 minutes until wilted. Continue over medium-low to medium heat, stirring every few minutes, until the onions are soft, jammy and a uniform rich gold, about 60–120 minutes total. Stir more often near the end; lower the heat if the edges darken before the centers soften. Do not stop at pale, simply softened onions.

3. 3

   Step 3. Whenever brown residue threatens to scorch, add 2 tablespoons of the measured water and scrape it into the onions. Let that water evaporate before continuing. Use up to 1 cup as needed. Aim for sweet-smelling golden onions and brown fond, never blackened bits; use color and softness rather than the clock.

4. 4

   Step 4. Stir in the garlic for 30 seconds, then the flour for 1 minute. Gradually add the stock, scraping the bottom. Add the thyme, bay leaf and pepper. Bring to a simmer and cook gently for 20 minutes. Remove the bay leaf and stir in the vinegar to balance the onions’ sweetness.

5. 5

   Step 5. During the final simmer, heat the oven to 425°F. Arrange the baguette on the sheet pan and toast for 5–7 minutes, turning once. Divide the cheese over the slices. Switch to the broiler and broil about 6 inches from the element for 1–3 minutes, watching constantly, until bubbling and lightly browned.

6. 6

   Step 6. Divide the soup among four bowls and top each with two cheese toasts. Serve carefully; the soup and melted cheese are very hot. Refrigerate leftovers promptly in shallow containers, within 2 hours (1 hour above 90°F), at 40°F or below. Use within 3–4 days; reheat to 165°F.