Savory Crockpot French Onion Soup

Coming up with cozy dinner ideas during the cold winter months can feel like an endless challenge. Between juggling work deadlines, after-school activities, and trying to keep the house warm, the last thing anyone wants is to spend hours standing over the stove stirring a pot of soup.

That’s why this crockpot French onion soup has become my go-to recipe for busy weeknights: it’s hands-off, deeply comforting, and fills the house with wonderful aromas while it simmers away in the slow cooker all day long.

What Kind of Onions Should I Use?

While this recipe calls for white onions, you actually have several good options when making French onion soup. White onions give you a clean, sharp flavor, but yellow onions work just as well and are often even preferred since they get super sweet when caramelized. Sweet onions like Vidalia could work too, though they might make your soup a bit too sweet when combined with the brown sugar. Just make sure to slice your onions nice and thin – about 1/8 inch thick is perfect – so they’ll break down properly during cooking. If you’re in a hurry, you can use a mandoline to get those thin, even slices, but a sharp knife works just fine too.

Options for Substitutions

Let’s talk about what you can swap in this cozy soup recipe if needed:

• White onions: You can use yellow onions, sweet onions, or even red onions instead. Each type will give a slightly different flavor, with sweet onions making a milder soup and red onions adding a bit more bite.
• Dry sherry: No sherry? Try dry white wine, or for a non-alcoholic option, use additional beef broth with a splash of apple cider vinegar to add that slight tang.
• Gruyere and Emmental cheese: While these Swiss-style cheeses give the most authentic flavor, you can use regular Swiss cheese, provolone, or even mozzarella. Just make sure to pick a cheese that melts well.
• French bread: Any crusty bread works here – sourdough, Italian bread, or even regular sandwich bread in a pinch. Just toast it first if it’s not stale.
• Fresh thyme: Dried thyme works fine – use 1 teaspoon as noted. You could also try a mix of dried herbs like herbes de Provence if you have that on hand.
• Beef broth: While beef broth gives the best flavor, you can use vegetable broth for a vegetarian version. Just add a splash of soy sauce for extra depth.

Watch Out for These Mistakes While Cooking

The biggest mistake when making French onion soup in a crockpot is rushing the onion caramelization process – even in a slow cooker, properly caramelized onions need at least 8-10 hours on low to develop that rich, sweet flavor that makes this soup special. Another common error is using too much liquid at the start, as the onions will release their own moisture during cooking – begin with just enough broth to cover the onions, then add the remaining broth after they’ve caramelized. To prevent a watery soup, avoid lifting the lid during cooking unless absolutely necessary, as each peek can add 20-30 minutes to the cooking time and release valuable moisture. For the best cheese-topped finish, make sure your broiler-safe bowls are completely cool before adding the bread and cheese, and watch carefully under the broiler – the difference between perfectly golden and burnt is often just 30 seconds.

What to Serve With French Onion Soup?

While French onion soup is often enjoyed as a starter, it can easily become a complete meal with the right sides! A crisp green salad with a light vinaigrette dressing helps balance out the rich, savory flavors of the soup. For a more substantial meal, try serving it alongside a half sandwich – I particularly like pairing it with a simple ham and butter sandwich on a crusty baguette (very French!). If you’re hosting dinner, consider setting out a platter of roasted vegetables or steamed asparagus dressed with just a touch of olive oil and lemon juice to round out the meal.

Storage Instructions

Keep: This French onion soup base (without the bread and cheese) can stay fresh in the fridge for up to 4 days when stored in an airtight container. The flavors actually get better after a day or two as they continue to develop!

Freeze: Good news – this soup freezes really well! Pour the cooled soup (without bread and cheese) into freezer-safe containers or bags and it’ll keep for up to 3 months. Just leave a bit of space at the top since liquids expand when frozen.

Reheat: To serve, warm the soup on the stovetop over medium heat or in the microwave until hot. Then add fresh bread and cheese on top and broil until bubbly – this way you’ll get that perfect cheese pull every time! If reheating from frozen, thaw overnight in the fridge first.

Preparation Time	10-15 minutes
Cooking Time	360-480 minutes
Total Time	370-495 minutes
Level of Difficulty	Medium

Estimated Nutrition

Estimated nutrition for the whole recipe (without optional ingredients):

• Calories: 1800-2000
• Protein: 60-70 g
• Fat: 100-110 g
• Carbohydrates: 180-200 g

Ingredients

• 3 large white onions (sliced thinly)
• 3 tablespoons butter
• 2 tablespoons brown sugar
• 8 cups beef broth (reduced sodium preferred)
• 1 tablespoon worcestershire sauce
• 1 clove of garlic (finely minced)
• 1/3 cup dry sherry
• 4 sprigs fresh thyme (or 1 teaspoon dried thyme)
• 1 bay leaf
• 8 slices of french bread (preferably stale or dry)
• 3/4 cup gruyere cheese, shredded
• 1/2 cup emmental cheese, shredded
• 6 tablespoons parmesan cheese, shredded

Step 1: Caramelize the Onions

In a large non-stick pan, combine onions, butter, and brown sugar.

Cook these ingredients over medium-low heat, stirring occasionally, until the onions become golden and caramelized.

This process should take about 20 minutes and will develop a deep, rich flavor for the soup.

Step 2: Transfer to Slow Cooker

Once the onions are golden, carefully transfer them to the slow cooker.

Add the remaining ingredients to the slow cooker, ensuring everything is well combined, except for the bread and cheese.

These will be added later to complete the dish.

Step 3: Cook the Soup

Set your slow cooker to low and let the soup cook for 6 to 8 hours.

This slow cooking process allows all the flavors to meld together, resulting in a rich and hearty soup.

Ensure you stir occasionally to keep all the ingredients well mixed.

Step 4: Prepare for Serving

After the cooking time has completed, remove and discard the bay leaf from the soup.

Ladle the soup into bowls, preparing them for the topping.

This will be the base for the final, delectable layer of cheese and bread.

Step 5: Broil with Bread and Cheese

Top each bowl of soup with a slice of dry bread and a generous amount of cheese.

Place the bowls under a broiler for 2 to 3 minutes, or until the cheese is melted and browned to your preference.

Be sure to watch closely to avoid burning.

This step adds an irresistible finishing touch to your soup.

Step 6: Serve Hot

Carefully remove the bowls from the broiler, as they will be hot.

Serve the soup immediately while the cheese is bubbly and fresh from the oven.

Enjoy the rich, comforting flavors of this slow-cooked delight!