Description
This Slow Cooker French Onion Soup recipe offers a rich and comforting classic French dish perfectly cooked using a slow cooker. Caramelized onions are slowly cooked with herbs, beef broth, and a hint of sweetness, then topped with toasted garlic baguette slices and melted Swiss and Parmesan cheeses. Ideal for a warming meal that requires minimal hands-on time and delivers deep, layered flavors.
Ingredients
Scale
Soup Base
- 1 stick butter
- 5 sweet yellow onions, sliced (white, yellow, or red onions can be used)
- 1 tsp salt
- 1/4 tsp pepper
- 1/4 cup flour
- 64 oz beef broth or beef stock (two 32-oz. containers)
- 1 tsp sugar (optional, only if onions are not sweet)
- 2 tsp minced garlic
- 1/4 tsp dried thyme (not ground)
- 1/4 tsp dried oregano (not ground)
- 1 tsp Worcestershire sauce
- 1 Tbsp balsamic vinegar
- 1 bay leaf
Croutons & Toppings
- 1 baguette
- Olive oil (for brushing)
- 1 whole garlic clove (for rubbing on toasted bread)
- Sliced Swiss cheese (about 2 slices per serving; can use provolone or gruyere)
- Shredded Parmesan cheese (about 1 tablespoon per serving)
Instructions
- Caramelize Onions: In a large skillet over medium-high heat, melt the butter. Add the sliced onions and sprinkle with salt and pepper. Sauté the onions, stirring often, for about 10 minutes until browned and caramelized. Adjust heat as needed to prevent burning.
- Add Flour: Stir the flour into the butter and caramelized onions and cook for 2 minutes to form a roux, which will help thicken the soup.
- Transfer to Slow Cooker: Pour the floured onions into the slow cooker. Add beef broth, sugar if using, minced garlic, dried thyme, dried oregano, Worcestershire sauce, balsamic vinegar, and place the bay leaf on top. Stir well to combine all ingredients.
- Cook Soup: Cover and cook on HIGH for 4 hours or on LOW for 8 hours to allow the flavors to meld together thoroughly.
- Prepare Croutons: Preheat oven to 500°F with the broiler setting. Slice the baguette into 1/4-inch slices and arrange on a sheet pan. Brush each slice lightly with olive oil using a pastry brush. Broil for 3-5 minutes or until toasted and browned. Once toasted, rub each slice with the cut side of a garlic clove to infuse garlic flavor.
- Assemble Bowls: Remove the bay leaf from the soup. Ladle the soup into ovenproof bowls placed on a sheet pan or pie tin. Top each bowl with several homemade croutons, 1-2 slices of Swiss cheese (or provolone/gruyere), and sprinkle with shredded Parmesan cheese.
- Broil to Finish: Place the bowls under the broiler until the cheese melts, bubbles, and turns golden brown, creating a delicious cheesy crust on top.
Notes
- Onions can be white, yellow, or red depending on availability, but sweet yellow onions are preferred for natural sweetness.
- Sugar is optional and only necessary if your onions are not sweet enough to balance the flavors.
- Use ovenproof bowls for broiling the cheese topping safely.
- If you prefer a vegetarian version, substitute beef broth with vegetable broth but keep in mind the flavor profile will differ.
- Adjust seasoning with additional salt and pepper at the end if necessary.
- Broiling time may vary depending on your oven, watch closely to prevent burning the cheese.
