Slow Cooker French Onion Soup

Let your slow cooker do the magic while you cozy up under a blanket. This slow cooker French onion soup is rich, cheesy, and tastes like it simmered on grandma’s stove all day. Spoiler: it didn’t. But it sure tastes like it.

Why You’ll Love This Slow Cooker French Onion Soup

This soup is comfort in a bowl no standing over a stove or babying onions. Just toss it all in the slow cooker and come back to savory, golden perfection. It’s freezer-friendly too, so make a double batch and tuck some away for a rainy day. Whether you’re nursing a cold or just want to warm your soul, this one delivers. If you love set-it-and-forget-it meals, you’ve gotta try our slow cooker German potato soup with sausages next hearty, rustic, and pure winter magic.

What Is French Onion Soup?

French onion soup goes all the way back to 18th-century Paris a peasant dish turned café classic. It’s all about caramelized onions, rich beef stock, toasted bread, and bubbly cheese. Simple? Yes. But oh-so elegant once it hits your spoon. Want something with that same nostalgic charm? This village soup with a rustic twist is packed with cozy vibes and wholesome flavor.

Ingredients You’ll Need

3 tablespoons unsalted butter
3 pounds sweet onions, thinly sliced
1 tablespoon brown sugar
2 cloves garlic, minced
6 sprigs fresh thyme
2 bay leaves
8 cups beef stock (or vegetable stock for a meatless version)
2 tablespoons sherry vinegar
Salt and black pepper to taste
1 baguette, sliced
2 cups shredded Gruyère cheese
1/2 cup grated asiago (or Swiss/fontina)

Craving a creamy soup instead? This creamy chicken lasagna soup is like a hug in a bowl dreamy for weeknights.

How to Make French Onion Soup in the Slow Cooker

Step-by-Step Instructions

1. Add the butter, onions, brown sugar, and garlic to your slow cooker. Stir well.
2. Add thyme and bay leaves. Cover and cook on low for 8 hours, until the onions are deep golden and fragrant.
3. Stir in the beef stock and sherry vinegar. Season with salt and pepper. Cover and cook for another 2 hours on low.
4. Meanwhile, preheat your oven broiler. Place baguette slices on a baking sheet and toast each side until crisp.
5. Ladle the soup into oven-safe bowls. Place a toasted baguette slice on top of each, then pile on the cheese.
6. Broil until cheese is melted, bubbly, and golden keep an eye on it, it happens fast!
7. Serve hot and cheesy, with a little thyme if you’re feeling fancy.

Visual Tips

Use a mandoline if you want ultra-thin onion slices with zero tears
When onions turn deep amber and smell caramel-sweet, they’re ready
Don’t skip the broiler! It’s the cheesy crown jewel

Tips for the Best Flavor

Sweet onions (like Vidalia) caramelize like a dream
Use a high-quality stock for depth it’s the soul of the soup
Add fresh herbs early but remove them before broiling
Toast your bread first so it doesn’t get soggy
Don’t skimp on cheese it’s not the time for restraint!

What to Serve With It

This soup shines on its own, but pairings make it a meal:
A crisp Caesar or chopped Italian salad
Roasted Brussels sprouts or sweet potatoes
A few slices of crusty garlic bread if you’re leaning all-in
Want a heartier companion? Serve it alongside this rustic cabbage roll soup for the ultimate cozy night in.

Storing & Freezing Instructions

Fridge: Store leftovers in airtight containers for up to 4 days. Keep the bread and cheese separate for best texture
Freezer: Freeze just the soup (no bread or cheese) for up to 3 months
Reheat: Warm gently on the stove, then top with fresh bread and cheese before broiling

Recipe Variations & Swaps

Vegetarian? Use veggie broth and skip the cheese for a vegan version
No sherry vinegar? White wine or apple cider vinegar works great
Gruyère too fancy? Try Swiss, provolone, or even mozzarella
Swap baguette for crusty sourdough or French bread

Frequently Asked Questions

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