Crockpot French Onion Soup

There’s nothing better than coming home to a steaming bowl of French onion soup covered in melted cheese on a chilly evening. This comfort food classic is loaded with silky strands of caramelized onion swimming in a delectable broth. Then it’s topped with cheesy slices of French bread for one of the most satisfying soups you’ll ever tuck into. The only problem? It’s quite a labor-intensive dish.

Low and slow is usually the name of the game when it comes to caramelizing onions—and it still is for this recipe, only we’re letting the slow cooker do the heavy lifting. Making sure the onions don’t brown too quickly or stick to the bottom of a pan involves constant stirring. The Crockpot is the hands-free answer to a delicious, heart-warming French onion soup that doesn’t require you to hole up in your kitchen for hours.

With a few pantry staples, easily accessible ingredients and one trusty appliance, you’ll master our Crockpot French onion soup recipe and never make this soup another way. 

Ingredients for Crockpot French Onion Soup

• Butter: You can’t caramelize onions for French onion soup without butter. We like high-fat European butter for this recipe, to get the best flavor, but lower-fat American butter will do if that’s what you have on hand. 
• Onions: A blend of sweet onion (like Vidalia, Maui Sweets and Walla Walla Sweets) and sharp red onion is the secret to the best-ever French onion soup, but it’s important to use a two-to-one ratio of sweet to red, otherwise the flavor would be too intense.  
• Condensed beef broth: Condensed, undiluted beef broth is also needed for the base of this soup. You can go the store-bought route with two cans, or make homemade beef broth and then boil it to reduce by half until it resembles more of a beef consomme.
• White wine: A dry white wine (like pinot grigio, chardonnay or sauvignon blanc) will help scrape up any remaining onion bits on the bottom of the slow cooker and keep the broth from being overly cloying from the sweetness of the caramelized onions. If you don’t have white wine or don’t want to use it, 3/4 cup of regular-strength beef broth is a perfectly fine substitute. 
• Herbs: Fresh herbs like thyme and parsley are a nice complement to French onion soup with their earthy peppery notes. A dried bay leaf also works its magic by deepening the soup’s flavors and adding complexity (just remember to remove it before serving). 
• Worcestershire sauce: The Worcestershire is good for a bit of umami—salty, sweet and spicy all at the same time.
• French bread: To use any other bread besides a baguette or crusty French bread would be criminal in this recipe for French onion soup in a slow cooker.
• Cheese: We love Gruyere for French onion soup. This French cheese is nutty, earthy and so good with the taste of caramelized onions in every bite, but you could also use Swiss cheese, raclette or Gouda as an alternative. 

Directions

Step 1: Caramelize the onions

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Place the cubed butter in a 5-quart slow cooker, top it with the sliced sweet and red onions, then sprinkle with a few cranks of freshly cracked pepper. Cook, covered, on low until the onions are tender, five to six hours.

Step 2: Stir in the liquids

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Once the onions are nice and caramelized, stir in the broth, water, wine, herbs and Worcestershire sauce. Place the lid back on and cook, covered, on low until the flavors are blended, two to three hours. Then remove the herb sprigs and bay leaf.

Step 3: Broil the baguette slices

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When you’re ready to serve, preheat the broiler and place the bread on a baking sheet. Broil the slices 4 inches from the heat until the baguette is lightly toasted, one to two minutes per side.

Step 4: Melt the cheese

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Top the bread with cheese and broil until it’s melted, one to two minutes, being careful not to let it burn. Divide the soup among eight bowls, top with the cheese toast and serve immediately.

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Crockpot French Onion Soup Variations

• Try a trifecta of cheeses: Instead of employing just one cheese for your toast topper, try a mix of three for deeper flavors. A French or alpine cheese like Gruyere or Swiss, an Italian cheese like melty mozzarella and a crumbly hard cheese like Parmesan work well together flavor-wise.
• Add more beef: Since the beef broth is so rich and hearty, French onion soup doesn’t usually have additional meat hidden inside, but who’s to say you can’t add some? Shredded short ribs, sauteed steak tips and browned ground beef would be great here and sneak in extra protein at the same time.
• Make it vegan: Thanks to dairy-free cheese and meat-free bone broth, it’s entirely possible to make a vegan version of slow-cooker French onion soup. Simply swap the butter for vegan butter or olive oil, the beef broth for vegetable broth and the Gruyere cheese for cashew cheese or your favorite vegan cheese.

How to Store Crockpot French Onion Soup

If you want to make the soup base ahead of time but only fire off the cheesy bread right before you’re going to serve it, then place the slow-cooker pot with the lid on in the refrigerator, or divvy up the soup into French onion soup crocks. You can also leave it in the slow cooker on warm until you’re ready to broil the cheesy croutons and serve.

Can you freeze French onion soup?

Absolutely! But we recommend only freezing the cooked onion soup in sealed airtight containers in the freezer, not the soup with the cheese or bread on top, as it can break down and get mushy when you go to thaw the soup.

How long does French onion soup last?

This soup will stay fresh in an airtight container with a lid—without the croutons—for three to four days in the refrigerator. In the freezer, it will last for three to four months.

How do I reheat French onion soup?

If frozen, let the soup thaw in the fridge overnight, or run the container under hot water until you’re able to remove the soup and transfer it to a saucepan. Then, slowly bring the soup to a boil and transfer it to bowls or crocks once it’s fully cooked through. Top with cheesy croutons and dig in.

Crockpot French Onion Soup Tips

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What’s the best cheese for French onion soup?

Gruyere cheese is delicious in this recipe. Its sweet, nutty flavor goes well with the oniony broth, and it melts wonderfully.

Can I broil the cheese toast on top of the soup?

You can, but we don’t recommend this. Toasting the bread with cheese separately, instead of broiling it on top of the soup in crocks, prevents the underside of the bread from becoming soggy.

How do you deepen the flavor of French onion soup?

Fresh herbs like thyme and a dried bay leaf help here. As does a splash or two of an umami-rich ingredient like Worcestershire sauce. You could also use fish sauce or apple cider vinegar for the same effect.

What’s the best way to eat French onion soup?

Use a fork and a knife to break through the cheesy toast, splitting it up into easier-to-eat sections. If you’re less concerned with etiquette, use the bread to sop up more onions and broth with your hand, the rustic way to enjoy this comfort food favorite.