Description
A rich and comforting French Onion Soup made effortlessly in the slow cooker. Sweet, caramelized onions are cooked low and slow, then simmered in beef broth with balsamic vinegar for deep flavor. Finished with toasted baguette slices and melty Gruyère cheese, this cozy classic delivers bistro-quality taste with almost no hands-on time.
Ingredients
- 3 lb yellow onions, peeled, sliced into quarter-moons
- 2 tbsp unsalted butter, melted
- 2 tbsp olive oil
- 2 tsp kosher salt, plus more to taste
- Freshly ground black pepper, to taste
- 10 cups reduced-sodium beef broth
- 2 tbsp balsamic vinegar
- 3 tbsp brandy (optional)
Instructions
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Caramelize Onions – Place onions in a 5-quart or larger slow cooker. Add butter, olive oil, salt, and pepper. Stir to coat. Cover and cook on LOW for 12 hours (overnight) until onions are dark golden-brown.
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Add Flavor Base – Stir in beef broth and balsamic vinegar. Cover and cook on LOW for another 6–8 hours. Adjust seasoning. Stir in brandy if using.
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Cheesy Finish – Preheat oven to 350°F (175°C). Ladle hot soup into oven-safe bowls on a baking sheet. Top each with baguette slices and Gruyère cheese.
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Bake & Broil – Bake for 20–30 minutes until cheese melts, then broil for 2–3 minutes until bubbly and golden. Cool slightly before serving.
Notes
Slice onions evenly for consistent caramelization.
Gruyère is traditional, but Swiss or provolone works too.
Freeze without bread and cheese topping for up to 3 months.
For vegetarians, use vegetable broth and skip brandy.
- Prep Time: 15 minutes
- Cook Time: 18–20 hours (slow cooker + baking time)
- Category: Soup
- Method: Slow Cooking
- Cuisine: French