Name: Classic Slow Cooker French Onion Soup Recipe
Prep time: 10 min
Cook time: 10 h
Total time: 10 h 10 min
Yield: 8
Cuisine: French
Ingredients: 2 pounds white onions, thinly sliced; 3 sprigs fresh thyme; 2 garlic cloves, minced; 1 bay leaf; 3 tablespoons unsalted butter; 1 tablespoon olive oil; 5 cups beef broth; 1 cup croutons; 1 cup shredded Gruyere cheese

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There is nothing as delicious as a rich bowl of French onion soup on a chilly day. The smell of this cooking is unlike any other soup, and while so very simple, it builds tremendous flavors that truly make your mouth water. This easy-to-follow recipe takes a while to make, but the result is absolutely delicious.

French Onion Soup

You've probably had onion soup in some variation in the past. We have a great basic onion soup recipe we have shared, but this recipe is that classic dish that you see in restaurants. A dark rich broth-based soup that is truly just onions and herbs. It is by far one of the easiest soups you will ever make.

Using the slow cooker makes it even easier, but remember this recipe takes at least 10 hours to slow cook. So, plan accordingly. It is best to make when you will be home to stir the mixture every few hours as well. So, a great weekend soup recipe for the fall and winter months.

And if you want something a bit heavier, check out this French onion soup casserole from Fanny Slater. It's a great choice for a meal rather than just a starter.

White bowl of soup on wooden board next to bowl of cheese

What is the Difference Between Onion Soup and French Onion Soup?

The biggest difference between an English onion soup and French onion soup is the broth base. French onion soup uses a beef broth or stock for a richer flavor. English onion soup will use any broth, including chicken or vegetable.

Image looking down into white bowl of soup topped with bread and cheese

What Cheese is On French Onion Soup?

Traditionally, Gruyere is used for French onion soup. If you cannot find or do not have it available currently, you can use quality Swiss cheese instead.

Some will recommend using mozzarella, but the richer flavor of Swiss, Parmesan, or Gruyere is part of the experience. So, while it can work in a pinch, I prefer to avoid mozzarella for this recipe.

TIP: Shred your own cheese for this for best melting results. Pre-shredded cheese will not give you the same richness or melty result.

French onion soup in white bowl topped with toasted bread and cheese

What Onions Should I Use?

You may see a basic white onion used most frequently, but you can use different onions and create different flavors.

If you want a bit more of that bitterness behind the sweetness, go with red onion. To create a brighter flavor with more sweetness, choose the yellow onion.

When in doubt a sweet onion will give a great flavor from the caramelization and still have that bit of bite you expect from the onion in this soup.

Two white ramkens of french onion soup on green tablecloth

Can I Use Croutons Instead of Toasted Bread?

While toasted bread is traditional, you can definitely use croutons with your soup. It makes serving just a bit easier, and there are a large variety of flavored croutons to choose from which add even more depth of flavor to every bite.

You may be used to your soup being served with the bread on top and cheese broiled over it, I prefer to serve the soup with the bread on the side for dipping.

Bowl of soup next to white napkin and bowl of cheese

How Much Dried Thyme Should I Use in Place of Fresh Thyme?

Each sprig of thyme usually contains 1 to 2 teaspoons of actual thyme leaves. When using dried herbs in place of fresh, you typically would use 1 teaspoon of dried for every 1 tablespoon fresh.

In this recipe, I would recommend using 1 teaspoon dried thyme in place of the 3 sprigs fresh recommended in the recipe.

Ingredients

White onions
Fresh thyme
Garlic cloves
Bay laef
Unsalted butter
Olive oil
Beef broth
Gruyere cheese
Croutons
Salt
Black pepper

Onions on green table with teal bowls of spices and butter

Handy Kitchen Tools

How to Make Homemade French Onion Soup

In a 6-quart slow cooker, place the onions, thyme, garlic, bay leaf, butter, olive oil, salt, and black pepper. Stir together.

Raw onions in black slow cooker with thyme and bay leaf

Cover with the lid and cook on high heat for 6 to 8 hours, stirring every few hours. The onions should be soft and caramelized. Browned but not burned.

Black slow cooker filled with browned onions

Add the beef broth and stir to combine. Continue cooking for an additional 3 hours on high heat.

Metal spoon of soup above black slow cooker

To serve, pour into oven-safe ramekins and top with croutons and shredded Gruyere cheese.

Broil for 1 to 2 minutes until cheese has melted and is just browning.

Melted cheese and toasted bread on top of white ramekin of onion soup

What Can I Do With Leftover French Onion Soup?

One of my favorite things about this recipe is that the leftovers are so versatile. French onion soup is good in the refrigerator for up to 4 days. I like to prepare it as part of a meal the first day, then use the leftovers for other recipes for one to two more meals.

Pour over chicken breasts then cover with cheese and bake for a "French onion chicken" meal.
Thicken with cornstarch to create a gravy for serving over potatoes.
Saute mushrooms and stir in to the soup for a higher protein version.
Use as the liquid in a mushroom gravy to serve over round steak or Salisbury steak.

More Soup Recipes

Soup is a great starter for a meal, but in many cases can become a perfect meal all by itself. If you are looking for more yummy soups to add to your meal plan, look no further. Below are some of my personal favorites that you are bound to love!

📖 Recipe

Yield: 8