French onion soup has a very special place in my heart. For many years, I would actually order it at every single restaurant I went to that offered it, just to compare and determine which versions I liked best. You'd be surprised how many restaurants offer sodium-heavy broth with giant chunks of onion within. There needs to be more finesse in making a proper French onion soup.
The onions should be slowly cooked and caramelized until they are dark golden and almost falling apart. I like to lightly salt my onions right off the bat, because it allows them to begin releasing water immediately. I also cover the pot to really allow them to sweat and soften before any browning even begins.
I finish caramelizing them uncovered. It can be a time consuming process (and your onions will shrink like crazy--I started with over half the pot full of onions and ended up with a thin layer along the bottom), but it's really worth it to develop the wonderful onion flavor prevalent in this soup.
Many onion soups feature already soggy bread, which does fall apart beneath the cheese and soak up lots of the yummy broth, but I prefer having at least the surface of that bread still boast a bit of a crust. Anything beneath the surface absorbs soup and softens, but I like a bit more texture with my croutons.
The cheese on French onion soup is probably the most popular aspect. Traditionally, it's Gruyere, and sometimes Emmentaler (Swiss) grated over the top. I've seen many restaurants use a round of Provolone cheese, which I'll admit is the perfect shape to top the soup, and also offers nice flavor. I've seen Irish or English onion soup recipes use Cheddar to top the whole thing off. That's not a bad idea either, but I will stick to my beloved Gruyere for this round.
French Onion Soup
4 to 6 servings
4 tablespoons unsalted butter
6 cups sliced onions (About 3 to 4 onions, depending on size)
2 garlic cloves, finely chopped
2 bay leaves
1 cup red wine
1/4 cup all-purpose flour
2 quarts beef broth or stock
Freshly ground black pepper
About 1/2 a baguette (or other crusty bread), sliced and toasted (if using a baguette, slice on the bias to create more surface area)
8 ounces grated Gruyere
Melt the butter in a large pot over medium heat. Add the onions, season with salt, and mix to coat evenly with the butter. Cover the pot and allow the onions to sweat and soften, stirring occasionally for about 15 to 20 minutes. Continue cooking, uncovered, stirring occasionally, until the onions are caramelized, an additional 20 to 30 minutes.
Add the garlic and bay leaves, and saute for a couple minutes until fragrant. Add the wine, bring to a boil, and reduce the heat and simmer until most of the wine has evaporated, about 5 minutes. Dust the onions with the flour and cook for another 5 minutes with the heat on medium low, as to not burn the flour. Now slowly whisk in the beef broth being careful to smooth out any lumps. Season with salt and pepper, increase the heat to high, slightly cover the pot and bring the soup back to a boil. Reduce the heat to medium, and simmer uncovered for 10 more minutes. Discard the bay leaves. Adjust seasoning as needed.
When you're ready to eat, preheat the broiler. Ladle soup into oven-proof bowls. Float a couple baguette slices (or one large piece of toasted crusty bread) in each bowl on top of the soup. Sprinkle the slices with the Gruyere and broil until bubbly and golden brown, 3 to 5 minutes.
If you don't have oven-proof bowls, you can arrange the lightly toasted baguette slices on a sheet pan, sprinkle the cheese over the top of each slice, and broil as directed above. Then float the Gruyere croutons on top of the soup in each bowl.