French Onion Soup

Name: French Onion Soup (Slow Cooker)
Prep time: 15 min
Cook time: 8 h 30 min
Total time: 8 h 45 min
Yield: 4 servings
Cuisine: French
Ingredients: 3 large white onions, sliced into rings; 1/2 cup butter, sliced; 4 sprigs fresh thyme; salt, to taste; black pepper, to taste; 32 oz beef broth; 1 tbsp balsamic vinegar; 4-6 slices baguette, toasted; 6 oz Gruyère cheese, shredded

This slow cooker French onion soup caramelizes onions to deep sweetness and pairs them with beef broth, topped with crusty bread and melted Gruyère cheese. The hands-off cooking method delivers restaurant-quality results without constant stirring.

⚡Slow Cooker

🌍French 🏷️French onion soup 🏷️Soup 🏷️Slow cooker 🏷️Caramelized onions Gruyere cheese

🏷️

🏷️Comfort food

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TikTok

Total

8h 45m

Servings

4

Difficulty

Easy

Est. Cost

$19–$31

Recipe Source

View original recipe

From TikTok

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TikTok

Ingredients

3 large white onions, sliced into rings
1/2 cup butter, sliced
4 sprigs fresh thyme
salt, to taste
black pepper, to taste
32 oz beef broth
1 tbsp balsamic vinegar
4-6 slices baguette, toasted
6 oz Gruyère cheese, shredded

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Instructions

1
Place the sliced onions in the bottom of a slow cooker.
2
Top the onions with sliced butter and fresh thyme sprigs.
3
Season generously with salt and black pepper.
4
Cover and cook on low for 8-10 hours or on high for 4-5 hours, until the onions are deeply caramelized and soft.
5
Once caramelized, pour in the beef broth and balsamic vinegar. Stir to combine.
6
Cover and cook on high for another 30-60 minutes to allow the flavors to meld and the soup to heat through.
7
Preheat your oven's broiler. Ladle the hot soup into oven-safe bowls.
8
Place a slice of toasted baguette on top of the soup in each bowl.
9
Top generously with shredded Gruyère cheese.
10
Place the bowls on a baking sheet and broil for 2-3 minutes, or until the cheese is melted, bubbly, and slightly browned. Watch carefully to prevent burning.

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Tips & Notes

Pro tips

Slice onions into thin rings for faster caramelization and even cooking throughout the slow cooker cycle.
Use fresh thyme sprigs tied together or in a cheesecloth sachet for easy removal after cooking.
Toast baguette slices under the broiler just before serving to prevent them from becoming soggy in the hot broth.
Spread shredded Gruyère on toasted bread and broil 1–2 minutes until bubbly and golden before floating on the soup.

Substitutions

Butter → olive oil (use 1/4 cup; soup will be lighter)
Beef broth → vegetable or chicken broth (flavor will be milder; reduce salt slightly)
Baguette → focaccia or ciabatta (crust and density similar; toast well to avoid sogginess)
Fresh thyme → 1 tsp dried thyme (use half the amount; add at the start of cooking)

Storage & make-ahead

Store cooled soup in an airtight container in the refrigerator for up to 3 days. Reheat gently on the stovetop over medium-low heat; add fresh bread and cheese topping when serving to maintain crunch.

Equipment

slow cooker

Common Questions

Can I make French onion soup without a slow cooker?

Yes. Caramelize the sliced onions in a large pot over medium heat for 40–50 minutes, stirring occasionally, then add broth and simmer for 30 minutes. The slow cooker simply removes the active stirring.

What cheese can I use instead of Gruyère?

Swiss cheese or aged cheddar work well. Avoid soft cheeses; use firm, melting varieties for best results on top of the soup.

Can I make this soup ahead?

Yes. Make the soup (without the bread and cheese topping) up to 3 days ahead, store in an airtight container in the refrigerator, and reheat gently on the stovetop. Add fresh bread and cheese when serving.