Traditional Slow Cooker Onion Soup

Name: Traditional Slow Cooker Onion Soup
Prep time: 15 min
Cook time: 8 h
Total time: 8 h 15 min
Yield: 6 servings
Ingredients: 4 large yellow onions, thinly sliced; 2 tablespoons unsalted butter; 8 cups beef broth; 2 tablespoons olive oil; 1 tablespoon Worcestershire sauce; 1/2 teaspoon salt; 1/4 teaspoon black pepper; 1 bay leaf; 1 teaspoon fresh thyme leaves; 1 baguette, sliced; 2 cups grated Gruyère cheese

🕒 Prep: 15 min

🔥 Cook: 8 hours

🍽 Serves: 6

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This Traditional Slow Cooker Onion Soup is a comforting classic that warms the soul and fills the kitchen with an irresistible aroma. Perfect for chilly evenings, this recipe brings out the deep, savory flavors of caramelized onions in a rich broth, topped with melted Gruyère cheese. It's a simple yet elegant dish that feels like a warm hug in a bowl.

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Ingredients for Traditional Slow Cooker Onion Soup

Yellow onions are the star of the show, providing a sweet and savory base when caramelized. Butter and olive oil work together to help the onions achieve that perfect golden brown color without burning. Beef broth gives the soup a deep, meaty flavor that pairs wonderfully with the sweetness of the onions. Worcestershire sauce adds a hint of umami, enhancing the overall depth of the soup. A touch of salt and black pepper balances the flavors, while a bay leaf and fresh thyme bring subtle herbal notes. Baguette slices topped with Gruyère cheese create that classic, irresistible finish.

Tips & Tricks

If your onions are sticking while caramelizing, add a splash of water to deglaze the pan.
For a vegetarian version, substitute beef broth with vegetable broth.
Gruyère can be substituted with Emmental or Swiss cheese if needed.
Make sure your oven-safe bowls are truly oven-safe to prevent any accidents.

Serving Suggestions

This soup is a meal on its own but pairs wonderfully with a simple green salad dressed with a light vinaigrette. A glass of crisp white wine complements the rich flavors of the soup, making it a perfect dinner party starter or a cozy night in.

Frequently Asked Questions

Can I use a different type of onion?: While yellow onions are preferred for their sweetness, white onions can work in a pinch. Avoid red onions as their flavor is too sharp for this soup.
How long does this soup keep?: Stored in an airtight container, this soup will last in the refrigerator for up to 3 days. It also freezes well for up to 3 months.

Traditional Slow Cooker Onion Soup Recipe Walkthrough

Start by melting the butter and olive oil in a skillet over medium heat. Once they're nicely combined and sizzling, add the onions. Stir occasionally, letting the onions slowly caramelize to a rich golden brown over about 15 minutes. Patience is key here—let them develop their sweetness without rushing.

Once your onions are beautifully caramelized, transfer them to your slow cooker. Pour in the beef broth, then add the Worcestershire sauce, salt, pepper, bay leaf, and thyme. Stir everything together, ensuring the flavors are well distributed.

Cover the slow cooker and set it to cook on low for 6-8 hours. During this time, the flavors will meld together, and the onions will become incredibly tender. It's a perfect dish to start in the morning and come home to a delicious, ready-to-serve soup.

When you're almost ready to eat, preheat your broiler. Ladle the soup into oven-safe bowls, then place a slice of baguette on top of each serving. Generously sprinkle with Gruyère cheese. Place the bowls under the broiler for about 2-3 minutes, just until the cheese is melted and bubbly. Watch closely to avoid burning.

Why You'll Love This Recipe

Easy to prepare, letting the slow cooker do most of the work.
Rich, savory flavors that develop beautifully over time.
Perfect for meal prep — tastes even better the next day.
Crowd-pleaser that feels gourmet without the fuss.

Ingredients

4 large yellow onions, thinly sliced

2 tablespoons unsalted butter

8 cups beef broth

2 tablespoons olive oil

1 tablespoon Worcestershire sauce

1/2 teaspoon salt

1/4 teaspoon black pepper

1 bay leaf

1 teaspoon fresh thyme leaves

1 baguette, sliced

2 cups grated Gruyère cheese

Step-by-step Instructions

1. Melt butter and olive oil in a skillet over medium heat. Add onions and cook until caramelized, about 15 minutes.

2. Transfer caramelized onions to slow cooker. Add beef broth, Worcestershire sauce, salt, pepper, bay leaf, and thyme.

3. Cover and cook on low for 6-8 hours or until onions are tender and flavors meld.

4. Preheat broiler. Ladle soup into oven-safe bowls, top with baguette slices, and sprinkle with Gruyère cheese.

5. Place bowls under the broiler until cheese is melted and bubbly, about 2-3 minutes.

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