Best French Onion Soup

Use a Dutch oven with at least a 7-quart capacity for this recipe. Sweet onions, such as Vidalia or Walla Walla, will make this recipe overly sweet. Note that the entire process for caramelizing the onions takes 45 to 60 minutes. Use broiler-safe crocks and keep the rim of the bowls 4 to 5 inches from the heating element to obtain a proper gratinée of melted, bubbly cheese. If using ordinary soup bowls, sprinkle the toasted bread slices with Gruyère and return them to the broiler until the cheese melts, then float them on top of the soup.

1. FOR THE SOUP: Adjust oven rack to lower-middle position and heat oven to 400 degrees. Generously spray inside of Dutch oven with vegetable oil spray. Add onions, butter, and 1 teaspoon salt. Cook, covered, for 1 hour (onions will be moist and slightly reduced in volume). Remove pot from oven and stir onions, scraping bottom and sides of pot. Return pot to oven with lid slightly ajar and continue to cook until onions are very soft and golden brown, 1-1⁄2 to 1-3⁄4 hours longer, stirring onions and scraping bottom and sides of pot after 1 hour.
2. Carefully remove pot from oven (leave oven on) and place over medium-high heat. Cook onions, stirring frequently and scraping bottom and sides of pot, until liquid evaporates and onions brown, 15 to 20 minutes (reduce heat to medium if onions brown too quickly). Continue to cook, stirring frequently, until bottom of pot is coated with dark crust, 6 to 8 minutes, adjusting heat as necessary. (Scrape any browned bits that collect on spoon back into onions.) Stir in 1⁄4 cup water, scraping pot bottom to loosen crust, and cook until water evaporates and pot bottom has formed another dark crust, 6 to 8 minutes. Repeat process of deglazing 2 or 3 more times, until onions are very dark brown. Stir in sherry and cook, stirring frequently, until sherry evaporates, about 5 minutes.
3. Stir in 2 cups water, chicken broth, beef broth, thyme, bay leaf, and 1⁄2 teaspoon salt, scraping up any final bits of browned crust on bottom and sides of pot. Increase heat to high and bring to simmer. Reduce heat to low, cover, and simmer 30 minutes. Remove and discard herbs and season with salt and pepper to taste.
4. FOR THE CHEESE CROUTONS: While soup simmers, arrange baguette slices in single layer on rimmed baking sheet and bake until bread is dry, crisp, and golden at edges, about 10 minutes. Set aside.
5. TO SERVE: Adjust oven rack 7 to 8 inches from broiler element and heat broiler. Set 6 broiler-safe crocks on rimmed baking sheet and fill each with about 1-3⁄4 cups soup. Top each bowl with 1 or 2 baguette slices (do not overlap slices) and sprinkle evenly with Gruyère. Broil until cheese is melted and bubbly around edges, 3 to 5 minutes. Let cool 5 minutes before serving.
   TO MAKE AHEAD: Onions can be prepared through step 1, cooled in pot, and refrigerated for up to 3 days before proceeding with recipe. Soup can be prepared through step 3 and refrigerated for up to 2 days.

QUICKER FRENCH ONION SOUP
This variation uses a microwave for the initial cooking of the onions, which dramatically reduces the cooking time. The soup’s flavor, however, will not be quite as deep as with the stovetop method. If you don’t have a microwave-safe bowl large enough to accommodate all of the onions, microwave in a smaller bowl in 2 batches.
Combine onions and 1 teaspoon salt in large bowl and cover with large plate (plate should completely cover bowl and not rest on onions). Microwave for 20 to 25 minutes until onions are soft and wilted, stirring halfway through cooking. (Use oven mitts to remove bowl from microwave and remove plate away from you to avoid steam.) Drain onions (about 1⁄2 cup liquid should drain off) and proceed with step 2, melting butter in Dutch oven before adding wilted onions.