Slow Cooker French Onion Soup

 

Slow Cooker French Onion Soup: A Cozy Classic Made Easy

When the days get cooler and you’re craving something warm, rich, and comforting, there’s nothing quite like a bowl of French Onion Soup. And what makes this classic even better? Letting your slow cooker do most of the work. This Slow Cooker French Onion Soup is deeply flavorful, thanks to slowly caramelized onions, hearty beef broth, and a generous topping of crusty bread and melted cheese. It’s a simple yet elegant dish that feels like a hug in a bowl.

Why You’ll Love This Recipe

• Hands-off cooking: The slow cooker takes care of caramelizing the onions and simmering the soup — no standing over the stove for hours.

• Rich, deep flavor: Low and slow cooking brings out the natural sweetness of the onions and infuses the broth with intense savory depth.

• Perfect for meal prep: Make a big batch and enjoy leftovers for days. It reheats beautifully!

• Impressive but easy: Serve it to guests and they’ll think you spent all day in the kitchen.

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Ingredients

• 4 large yellow onions, thinly sliced

• 3 tablespoons butter

• 1 tablespoon olive oil

• 2 teaspoons sugar (to help caramelize the onions)

• 1 teaspoon salt

• 4 cloves garlic, minced

• 8 cups beef broth (low sodium preferred)

• ½ cup dry white wine (optional but adds depth)

• 1 tablespoon Worcestershire sauce

• 1 teaspoon fresh thyme (or ½ tsp dried thyme)

• Freshly ground black pepper, to taste

• 1 baguette, sliced into rounds

• 2 cups shredded Gruyère cheese (or Swiss, if preferred)

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Instructions

1. Prepare the onions

In a large skillet over medium heat, melt butter and olive oil. Add sliced onions, sugar, and salt. Cook, stirring occasionally, until onions are soft and golden brown (about 20–25 minutes). This step jump-starts the caramelization process.

Tip: You can skip this stovetop step and place raw onions directly in the slow cooker, but pre-caramelizing enhances flavor.

2. Load up the slow cooker

Transfer the caramelized onions to the slow cooker. Add garlic, beef broth, white wine (if using), Worcestershire sauce, thyme, and black pepper. Stir to combine.

3. Cook low and slow

Cover and cook on low for 6–8 hours, or on high for 3–4 hours. The longer, the better—the flavors only deepen with time.

4. Toast the bread

Near the end of the cooking time, preheat your oven to 375°F (190°C). Arrange baguette slices on a baking sheet and toast for 8–10 minutes, or until golden and crisp. For extra flavor, rub them with a cut garlic clove after toasting.

5. Assemble and broil

Ladle the hot soup into oven-safe bowls. Top each with a slice or two of toasted baguette and a generous handful of shredded cheese. Place bowls under the broiler for 2–3 minutes, or until the cheese is melted and bubbly.

No broiler-safe bowls? No problem. Place toasted bread on a baking sheet, top with cheese, and broil separately. Then float the cheesy bread on the soup.

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Serving Suggestions

Serve your Slow Cooker French Onion Soup with a crisp green salad, a glass of dry white wine, or just enjoy it on its own as a comforting main course. It's also a great starter for a cozy dinner party.

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Storage & Reheating

• Fridge: Store leftovers in an airtight container for up to 4 days.

• Freezer: Freeze the soup (without the bread/cheese) for up to 3 months.

• To reheat: Warm on the stove or in the microwave, then top with fresh toast and cheese.

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Final Thoughts

This Slow Cooker French Onion Soup is proof that gourmet doesn’t have to be complicated. It’s rustic, flavorful, and incredibly satisfying — the perfect dish to warm your soul on a chilly night. Whether you’re making it for a family dinner or a quiet night in, it’s sure to become a favorite in your soup rotation.