Slow Cooker French Onion Soup

This slow cooker french onion soup is one of those recipes that feels fancy but is actually really simple to make. The slow cooker does most of the work for you.

The key to a great french onion soup is letting the onions caramelize low and slow until they turn deep golden brown and sweet. That’s where all the flavor comes from.

Once the onions are ready, everything else comes together easily. You add broth, wine, and a few seasonings, then let it simmer for hours until the flavors really develop.

And of course, the best part is the toasted bread and melted cheese on top. It’s the thing that makes french onion soup so special.

If you’ve never tried making this at home, you’ll be surprised at how good it turns out. It’s honestly just as good as what you’d get at a restaurant.

What Makes This Recipe So Good

The Slow Cooker Does the Hard Part – Caramelizing onions on the stovetop means standing there stirring for 45 minutes, but this recipe lets your slow cooker handle all that low-and-slow caramelization while you go about your day.

Restaurant-Quality Flavor at Home – The combination of dry white wine, Worcestershire sauce, and hours of slow-cooked beef broth creates the kind of deep, rich, savory flavor you usually only get at a nice French bistro.

Deeply Caramelized Onions Make All the Difference – Cooking the onions uncovered on high for 3 to 4 hours draws out their natural sweetness and builds layers of flavor that you just cannot rush, and that patience is what separates a good French onion soup from an incredible one.

Ingredients

• 4 large Yellow Onions, thinly sliced
• 4 tbsp Unsalted Butter
• 3 cloves Garlic, minced
• 1 tsp Sugar
• 1/2 cup Dry White Wine
• 6 cups Beef Broth
• 1 tbsp Worcestershire Sauce
• 2 sprigs Fresh Thyme
• 2 Bay Leaves
• 1 tsp Salt
• 1/2 tsp Black Pepper
• 6 slices French Bread, about 1 inch thick
• 2 cups Shredded Gruyere Cheese

Directions

Step 1

Place the sliced onions and butter in the slow cooker. Sprinkle with the sugar and toss to coat. Cover and cook on high for 1 hour, then stir well.

Step 2

Continue cooking on high, uncovered, for another 3 to 4 hours, stirring occasionally, until the onions are deeply caramelized and golden brown.

Step 3

Stir in the minced garlic and white wine. Cook for 5 minutes to let the wine reduce slightly.

Step 4

Add the beef broth, worcestershire sauce, fresh thyme sprigs, bay leaves, salt, and black pepper. Cover and cook on low for 4 to 6 hours to let the flavors develop.

Step 5

Remove and discard the thyme stems and bay leaves. Taste and adjust seasoning.

Step 6

Ladle the soup into oven-safe bowls. Place a slice of french bread on top of each bowl and pile a generous amount of shredded gruyere cheese over the bread.

Step 7

Set the bowls on a baking sheet and broil on high for 2 to 3 minutes, until the cheese is melted, bubbly, and golden brown on top. Serve immediately.

Pro Tips

Keep the Lid Off for Caramelizing

The first hour with the lid on is just to get the onions softened and sweating. After that, cooking uncovered for 3 to 4 hours is what actually caramelizes them. If you keep the lid on the whole time, the moisture stays trapped and your onions will just steam instead of turning golden brown.

Stir them every 30 to 45 minutes during this uncovered phase. The edges of the slow cooker run hotter, so the onions around the sides will brown faster and can burn if you forget about them.

You want the onions to be a deep amber color, almost like the color of caramel candy. If they still look pale and wet after 4 hours, just keep going. It can take longer depending on your slow cooker.

Use the Wine to Deglaze

By the time the onions are caramelized, there will be dark sticky bits stuck to the bottom and sides of the slow cooker. When you pour in the white wine, use a wooden spoon to scrape all of that up. Those browned bits are packed with flavor and you don’t want to leave them behind.

If you don’t have dry white wine or don’t want to use alcohol, you can substitute a splash of white wine vinegar mixed with a little extra beef broth. It won’t be exactly the same, but it gives you that acidity that balances all the sweetness from the onions.

Toast the Bread Before Putting It on the Soup

Don’t just put raw french bread slices on top of the soup. They’ll soak through in seconds and turn into a soggy mess that sinks to the bottom. Instead, toast the bread slices in the oven at 375 F for about 5 to 7 minutes per side until they’re dry and lightly golden.

You want them crispy enough that they can sit on the surface of the soup and hold the weight of the cheese without falling apart. Stale bread from the day before actually works great here for the same reason.

Related Recipes

• Instant Pot Beef Stew
• Instant Pot Broccoli Cheddar Soup
• Instant Pot Chicken Noodle Soup
• Instant Pot Chili
• Instant Pot Mississippi Pot Roast

Frequently Asked Questions

What can I use instead of dry white wine?

If you do not want to use wine, you can substitute it with an equal amount of extra beef broth plus a splash of white wine vinegar or apple cider vinegar – about a teaspoon or so. The acidity mimics the brightness that wine brings to the soup.

Some people also use dry sherry or even a bit of apple juice with a squeeze of lemon. The main goal is to add a touch of acidity to balance out the sweetness of the caramelized onions, so any of these swaps work well.