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Bowl of Easy French Onion Soup topped with melted cheese and caramelized onions.

Easy French Onion Soup Cheesy Slow Cooker

A cozy, comforting French onion soup made effortlessly in a slow cooker, featuring sweet caramelized onions, rich broth, and melted cheese on top.
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Prep Time 15 minutes
Cook Time 10 hours
Total Time 10 hours 15 minutes
Servings: 4 servings
Course: Appetizer, Soup
Cuisine: French
Calories: 300
Ingredients Method Notes

Ingredients
  

Main Ingredients
  • 4-6 large Onions, sliced Yellow onions are recommended for best flavor.
  • 3 tablespoons Butter A splash of olive oil can be added.
  • 2-3 cloves Garlic, optional Add for extra flavor in the final 30 minutes.
  • 6 cups Beef broth Can use a mix of beef and chicken broth.
  • 1-2 teaspoons Worcestershire sauce, optional For added depth of flavor.
  • to taste Salt
  • to taste Pepper
  • Baguette slices Sturdy bread For topping.
  • to taste Cheese (Gruyere, Swiss, or mozzarella) For melting on top.

Method
 

Preparation
  1. Slice the onions and add them to the slow cooker with butter (and oil if using). Toss them around a bit.
  2. Cook on low for 8 to 10 hours or high for 4 to 6 hours until they are deep golden and jammy.
  3. Add garlic in the last 30 minutes if you want it a little softer and not too sharp.
Cooking
  1. Pour in broth, thyme, and Worcestershire sauce. Cook on low for an additional 1 to 2 more hours.
  2. Taste and adjust salt and pepper to your preference.
Serving
  1. Toast the bread, add cheese, and melt it in the oven or air fryer. Float the cheesy bread on your soup before serving.

Notes

This soup can be made vegetarian by substituting beef broth with rich vegetable broth and adding a splash of soy sauce or balsamic vinegar for flavor. Leftovers can be stored in the fridge for up to 4 days; bread and cheese should be stored separately to avoid sogginess. The soup freezes well, but it's best to freeze just the soup and reheat when needed.