French Onion Soup

Name: French Onion Soup (Slow Cooker)
Prep time: 10 min
Cook time: 4 h 15 min
Total time: 4 h 25 min
Yield: 6 servings
Cuisine: French
Ingredients: 4 large sweet onions, sliced; 1 tbsp butter; 1 tsp brown sugar; salt, to taste; black pepper, to taste; 2 tbsp all-purpose flour; 32 oz beef broth or bone broth; 4 slices bread; 1 cup shredded Gruyère cheese; 1 tbsp chopped green onions, for garnish

This slow cooker French onion soup combines caramelized sweet onions and rich beef broth, topped with toasted bread and melted Gruyère cheese for authentic French comfort in one pot.

⚡Slow Cooker

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

🏷️

🏷️Comfort food

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TikTok

Total

4h 25m

Servings

6

Difficulty

Easy

Est. Cost

$20–$33

Recipe Source

View original recipe

From TikTok

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TikTok

Ingredients

4 large sweet onions, sliced
1 tbsp butter
1 tsp brown sugar
salt, to taste
black pepper, to taste
2 tbsp all-purpose flour
32 oz beef broth or bone broth
4 slices bread
1 cup shredded Gruyère cheese
1 tbsp chopped green onions, for garnishoptional

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Instructions

1
Slice the sweet onions.
2
Add the sliced onions, butter, brown sugar, salt, and pepper to a slow cooker.
3
Cover and cook on high for about 4 hours, stirring every 30-60 minutes, until the onions are deeply caramelized.
4
Stir in the flour until it's fully incorporated with the caramelized onions.
5
Pour in the beef broth and stir to combine.
6
Cover and let the soup come to a simmer.
7
While the soup simmers, lightly toast the bread slices and cut them into small squares.
8
Arrange the toasted bread squares over the top of the soup in the slow cooker.
9
Sprinkle the shredded Gruyère cheese evenly over the bread.
10
Cover the slow cooker again and let the cheese melt for 5-10 minutes.
11
Garnish with chopped green onions, serve, and enjoy.

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Tips & Notes

Pro tips

Slice onions uniformly and stir occasionally in the slow cooker to ensure even caramelization and prevent browning on edges only.
Brown sugar accelerates caramelization and adds depth; don't skip it even though the amount seems small.
Toast bread slices separately in a 375°F oven for 5-7 minutes before topping with cheese to prevent them from becoming soggy in the soup.
Add cheese-topped bread to individual bowls just before serving, or broil the full pot for 2-3 minutes for a traditional crust effect.

Substitutions

Beef broth → bone broth or vegetable broth (vegetable broth yields lighter flavor)
Gruyère → Swiss, Emmental, or aged cheddar cheese
All-purpose flour → cornstarch (use 1.5 tsp for thickening)

Storage & make-ahead

Refrigerate soup in an airtight container for up to 4 days; reheat gently on stovetop and add fresh toasted bread and cheese topping before serving.

Equipment

slow cooker · oven (for toasting bread)

Common Questions

Can I make French onion soup without a slow cooker?

Yes. Sauté the onions in a Dutch oven over medium heat for 30-40 minutes until caramelized, then add broth and simmer for 20-30 minutes. The slow cooker method is more hands-off.

What type of onions work best?

Sweet onions like Vidalia caramelize best and develop deeper, sweeter flavor. Yellow onions also work well but take slightly longer to caramelize.

Can I substitute the Gruyère cheese?

Yes. Swiss, Emmental, or aged cheddar work as alternatives, though Gruyère's nutty flavor is traditional and ideal.

How long does French onion soup keep?

Store in an airtight container for up to 4 days. Reheat gently on the stovetop; add the bread and cheese topping fresh when serving to prevent sogginess.