This easy onion soup is a classic French recipe with a crisp bread and ooey-gooey cheese topping. In this version, condensed beef broth gives the soup its bold flavor. If the broth tastes too strong for your tastes, simply add more water. Or use a good quality homemade or store-bought beef stock, preferably low sodium. You can always taste and add extra salt before the soup is ready to serve.
A great-tasting onion soup takes time, so avoid making it if you are in a hurry. Caramelizing onions to a deep, rich, flavorful brown can take 45 minutes or longer. While it takes some time, the soup is easy to fix with just five ingredients and is so delicious and satisfying. This is an excellent soup to serve for lunch, and it’s hearty enough to serve for dinner with a tossed green salad or Caesar salad.
How to Make Perfect Caramelized Onions
If your soup bowls can stand the heat from the preheated broiler—made with sturdy stoneware, cast iron, or porcelain—you can broil the bread and cheese directly on the hot soup.
4 tablespoons unsalted butter
5 large yellow onions , thinly sliced
1 teaspoon salt
1 teaspoon granulated sugar
2 cloves garlic , minced
1/2 cup red wine
32 ounces low-sodium beef broth
24 ounces low-sodium chicken broth
1 tablespoon Worcestershire sauce
2 sprigs fresh thyme
1 bay leaf
1/2 tablespoon balsamic vinegar
pinch of salt and freshly ground black pepper , to taste
5 1-inch thick slices of French bread
2 tablespoons extra-virgin olive oil
1 1/2 cups shredded Gruyere Swiss cheese , room temperature
1/4 cup shredded Mozzarella cheese , room temperature
2 tablespoons finely grated Parmesan cheese , room temperature
In a large pot over medium-high heat, melt the butter. Add in the onions and sauté, stirring often, until softened, about 10 minutes.
Reduce heat to medium, stir in the salt and sugar; cook for another 35 minutes, stirring occasionally (every 5 minutes or so), until onions are caramelized and almost syrupy.
Add in the garlic and cook until fragrant, about 1 minute.
Pour in the red wine to deglaze the pot, scraping up any brown bits on the bottom and sides.
Add in the beef broth, chicken broth, Worcestershire sauce, thyme, and bay leaf.
Gently simmer over medium/medium-low heat for about 20 minutes, stirring occasionally.
Remove and discard the herbs.
Mix in vinegar and taste. Season with additional salt and pepper, if necessary.
Reduce heat to low, cover to keep hot while you prepare the bread.
Preheat oven broiler, with rack 6 inches from the heat source. Arrange bread slices on a baking sheet and brush both sides with the olive oil. Broil 2-3 minutes, flipping once, until well toasted on both sides. (NOTE: keep an eye on the bread the entire time to ensure it doesn’t burn. Every oven is different.) Remove from heat; leave broiler on.
Arrange oven safe bowls or crocks on a rimmed baking sheet. Fill each bowl 2/3 full with hot soup. Top each bowl with 1 slice toasted bread, and sprinkle with the Swiss, Mozzarella, and Parmesan cheeses.
Broil until bubbly and golden brown. As it softens, the cheese will fall over the sides of the crock and form a wonderful crusty seal.
Serve and enjoy!