How to Make French Onion Soup

Lindsay D. MattisonUpdated: Mar. 20, 2019

Our French onion soup recipe uses a slow cooker to shortcut the process without sacrificing any delicious flavor.

Growing up, my mother always made French onion soup on special occasions. It might seem like an odd thing to include on the Thanksgiving table, but it was my father’s favorite soup. Since the onions required hours of babysitting to prevent them from burning, Mom was only willing to make the dish a few times a year! If only she had known about our slow cooker method; she would have cooked it more often.

What’s in French Onion Soup?

This relatively simple soup is made from a base of butter, onions and beef broth. It has a rich and buttery flavor which is cut by melt-in-your-mouth tender onions that taste sweet after hours of caramelizing. Top each bowl with a cheesy crouton, and you’ve just created the ultimate comfort food!

What Is the Traditional Cheese Used in French Onion Soup?

Gruyère is the classic choice for creating the melted topping on French onion soup. This cave-aged Swiss cheese has a nutty flavor and melts beautifully. It’s readily available in most grocery stores, although it’s definitely not inexpensive. In our recipe, we use a mixture of Parmesan and mozzarella cheeses to get the ooey-gooey melted effect with a punch of salty, sharp flavor. You could also swap in some of our favorite lesser-known types of cheese, like Comté or Raclette.

How to Make French Onion Soup

Ingredients

1/2 cup butter
6 large onions, chopped
6 cans (10-1/2 ounces each) condensed beef broth, undiluted
1-1/2 teaspoons Worcestershire sauce
2 fresh thyme stems (or, 1/4 teaspoon dried thyme)
3 bay leaves
10 slices French bread, toasted
Shredded Parmesan and shredded part-skim mozzarella cheese—or Gruyère, if you fancy

Yield: 10 servings

Instructions

Step 1: Saute those onions.

The onions are the star of the show here, so start by giving them some color and texture. Heat the butter in a large skillet over medium-high heat. Add the onions and saute until they’re tender-crisp, about 10 minutes. Transfer the onions to a 5-quart slow cooker, making sure to scrape all the melted butter into the slow cooker with a rubber spatula.

Pro Tip: If you don’t have time for chopping onions, go ahead and slice them instead. The soup will be a bit chunkier, but it will taste just as delicious.

Step 2: Cook on low.

We love using the slow cooker for French onion soup because it’s impossible to burn the onions on accident! Add the beef broth, Worcestershire, thyme and bay leaves to the slow cooker and cook, covered, on low for 5 to 7 hours. When the onions are tender, it’s ready to serve!

Step 3: Melt the cheese and serve.

When you’re ready to eat, it’s time to create everyone’s favorite cheesy crouton. Preheat the broiler on High. Discard the thyme stems and bay leaves before ladling the soup into ovenproof bowls. Top each bowl with a slice of toast and sprinkle on the desired amount of cheese. Place the bowls on a baking sheet and slide them under the broiler. Broil for 2 to 3 minutes, until the cheese is lightly golden.

How Do You Make the Best French Onion Soup?

The slow cooker is our secret to success here. French onion soup on the stovetop requires what my mother called babysitting: a constant stirring of the caramelizing onions to prevent them from burning. By using the slow cooker, we make things fool-proof! You’ll still coax out all that sweet flavor, but you won’t have to spend hours making it happen.

You can also brighten up the soup before serving by adding a little citrus juice or vinegar. A teaspoon or two of cider vinegar tastes fantastic in this soup.

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