Slow Cooker French Onion Soup Recipe

Pittman & Davis

The history of onion soups can be traced back to Roman times. Onions were originally known as food for the common folk because they are easy to grow in large quantities. One of the most prominent modern onion soups originated in Paris during the 17th century. The exact inventor of this modern French dish is unclear and many have claimed to be the original creator.

The soup became more popular during the 1960’s, when French cuisine gained popularity in the United States. The dish is surprisingly easy to make but takes several hours of slow cooking to come out just perfect. The contrast between the caramelized onions, the beef broth, and cheese makes for a very appetizing starter which you can prepare in the morning, and thanks to the slow cooker, have ready for you when you come home for dinner.

How to make Slow Cooker French Onion Soup

For this recipe, you’ll need:

  • 6 tablespoons butter
  • 4 large Pittman 1015 onions, sliced and separated into rings
  • 1 tablespoon white sugar
  • 2 cloves garlic, minced
  • 1/2 cup cooking sherry
  • 7 cups reduced-sodium beef broth
  • 1 teaspoon sea salt, or to taste
  • 1/4 teaspoon dried thyme
  • 1 bay leaf
  • 8 slices of French bread
  • 1/2 cup shredded Gruyere cheese
  • 1/3 cup shredded Swiss cheese
  • 1/4 cup freshly shredded Parmesan cheese
  • 2 tablespoons shredded Mozzarella cheese


  1. Heat butter in a large, heavy pot over medium-high heat; cook and stir onions until they become translucent, about 10 minutes. Sprinkle onions with sugar; reduce heat to medium. Cook, stirring constantly, until onions are soft and browned, at least 30 minutes. Stir in garlic and cook until fragrant, about 1 minute.
  2. Stir sherry into onion mixture and scrape bottom of pot to dissolve small bits of browned food from the pot. Transfer onions into a slow cooker and pour in beef broth. Season to taste with sea salt; stir in thyme and bay leaf. Cover cooker, set on High, and cook 4 to 6 hours. If desired, set on Low and cook 8 to 10 hours.
  3. About 10 minutes before serving, set oven rack about 8 inches from the heat source and preheat the oven’s broiler. Arrange bread slices on a baking sheet.
  4. Broil bread slices until toasted, 1 to 2 minutes per side.
  5. Combine Gruyere, Swiss, Parmesan, and Mozzarella cheeses in a bowl, tossing lightly. Fill oven-safe soup crocks 3/4 full of onion soup and float a bread slice in each bowl. Top with about 2 tablespoons of cheese mixture per serving.
  6. Place filled bowls onto a baking sheet and broil until cheese topping is lightly browned and bubbling, about 2 minutes.

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