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Bowl of Slow Cooker French Onion Soup topped with melted Gruyere cheese and toasted bread.

Slow Cooker French Onion Soup

A cozy and comforting slow cooker version of classic French onion soup, topped with cheesy toasted bread for a delightful finish.
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Prep Time 15 minutes
Cook Time 9 hours
Total Time 9 hours 15 minutes
Servings: 6 servings
Course: Main Course, Soup
Cuisine: Comfort Food, French
Calories: 400
Ingredients Method Notes

Ingredients
  

Main Ingredients
  • 4 to 6 large Onions, thinly sliced Yellow onions are preferred for sweetness.
  • 3 to 4 tablespoons Butter For sautéing onions.
  • 6 to 8 cups Beef broth A mix of beef and chicken broth works too.
  • 1 leaf Bay leaf
  • 1 to 2 teaspoons Worcestershire sauce Optional for added depth of flavor.
  • to taste pinch Salt and pepper Adjust seasoning at the end.
  • 2 to 3 cloves Garlic, minced Optional but adds great flavor.
  • to taste teaspoon Thyme, dried or fresh
  • Baguette slices or any sturdy bread Bread For topping the soup.
  • to taste cups Cheese (Gruyere, Swiss, or mozzarella) For broiling on top.

Method
 

Preparation
  1. Add sliced onions to the slow cooker with butter and a pinch of salt. Stir to coat.
  2. Cook on low for 8 to 10 hours or on high for 4 to 6 hours, stirring when you can, until onions are deep golden and jammy.
  3. Add garlic (if using), thyme, bay leaf, broth, pepper, and Worcestershire sauce. Cook on low for an additional 2 hours to blend flavors.
  4. Taste and adjust salt, as broths vary significantly.
  5. Toast bread slices until crisp.
  6. Ladle soup into oven-safe bowls, top with toast, and sprinkle with plenty of cheese. Broil until bubbly and browned.

Notes

Leftover soup can be stored in the fridge and reheated, adding fresh toast and cheese each time for a treat.