Name: Slow Cooker French Onion Soup Recipe
Prep time: 10 min
Cook time: 29 h
Total time: 29 h 10 min
Cuisine: French
Ingredients: 3 pounds yellow onions, peeled, sliced, and cut into quarter-moons (about 4 large onions); 2 tablespoons unsalted butter, melted; 2 tablespoons olive oil; 2 teaspoons kosher or sea salt, plus more as needed when tasting soup; Freshly ground black pepper (optional); 8 cups (64 ounces) reduced-sodium beef broth; 2 tablespoons balsamic vinegar; 3 tablespoons cognac or brandy (optional); Baguette, sliced into 1-inch thick pieces (2-3 slices per bowl); 1/3 cup grated Gruyère cheese per bowl (about 2 cups total for 6-7 bowls)

Description

A rich and comforting Slow Cooker French Onion Soup featuring deeply caramelized onions, savory beef broth, and melted Gruyère cheese atop toasted baguette slices. This easy-to-make recipe uses a slow cooker to develop deep flavors over several hours, perfect for cozy meals.

Ingredients

Scale

Soup

3 pounds yellow onions, peeled, sliced, and cut into quarter-moons (about 4 large onions)
2 tablespoons unsalted butter, melted
2 tablespoons olive oil
2 teaspoons kosher or sea salt, plus more as needed when tasting soup
Freshly ground black pepper (optional)
8 cups (64 ounces) reduced-sodium beef broth
2 tablespoons balsamic vinegar
3 tablespoons cognac or brandy (optional)

Garnish

Baguette, sliced into 1-inch thick pieces (2-3 slices per bowl)
1/3 cup grated Gruyère cheese per bowl (about 2 cups total for 6-7 bowls)

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Instructions

Caramelize the Onions: Add the sliced onions, olive oil, melted butter, salt, and pepper (if using) to the slow cooker. Cook on low for about 14 hours, stirring 2-3 times during cooking if possible, until onions are deeply caramelized and golden brown.
Prepare the Soup: After the onions are caramelized, add the beef broth, balsamic vinegar, and cognac or brandy to the slow cooker. Stir well and cook on low for an additional 7-8 hours to allow the flavors to meld together.
Toast the Baguette Slices: About 10 minutes before serving, preheat the oven to 425°F (220°C). Arrange the baguette slices on a baking sheet and bake for 7-8 minutes until the bread is toasted and slightly crisp.
Assemble and Broil: Ladle the hot soup into oven-safe bowls. Place 2-3 toasted baguette slices on top of each bowl, then sprinkle 1/3 cup of grated Gruyère cheese over the bread. Arrange the bowls on a baking sheet for stability and place them in the oven. Bake for about 10 minutes until the cheese is melted and bubbly. Carefully remove from the oven and serve hot.

Notes

Stir the onions occasionally during caramelization to prevent burning and encourage even cooking.
The cognac or brandy is optional but adds a depth of flavor to the soup.
Use oven-safe soup bowls to broil the cheese safely in the oven.
To speed up toasting, you can broil the baguette slices but watch carefully to prevent burning.
For a vegetarian version, substitute vegetable broth for beef broth and omit alcohol.