Go Back
"Thinly sliced onions filling a white slow cooker on a kitchen countertop, ready to cook into sweet caramelized onions in a Crock-Pot."

Deeply caramelized onions

Deeply caramelized onions made overnight in the slow cooker turn into the richest, easiest French onion soup. Finished with toasted bread and bubbling Gruyère for classic bistro comfort at home.
Print Recipe Pin Recipe
Prep Time 20 minutes
Cook Time 10 minutes
2 minutes
Servings: 6
Course: Soup / Main
Ingredients Equipment Method Notes

Ingredients
  

  • 3 pounds yellow onions thinly sliced
  • 4 ounces butter melted
  • 4 cups beef broth
  • 1 cup dry white wine or more broth
  • 2 teaspoons fresh thyme
  • 2 bay leaves
  • Salt and pepper to taste
  • Crusty French bread slices
  • Gruyère cheese shredded

Equipment

  • Large slow cooker, large pot, oven-safe bowls, baking sheet, broiler

Method
 

  1. Place sliced onions in the crockpot. Pour melted butter over them and toss to coat.
  2. Cover and cook on LOW for 10–12 hours until deeply golden and caramelized.
  3. Transfer onions to a large pot. Add broth, wine, thyme, and bay leaves. Simmer 20–30 minutes. Season with salt and pepper. Remove bay leaves.
  4. Toast thick slices of French bread until crisp.
  5. Ladle soup into oven-safe bowls. Top with toasted bread and a generous amount of shredded Gruyère.
  6. Broil 3–4 minutes until cheese is melted, bubbling, and golden. Rest 1–2 minutes before serving.

Notes

Overnight low cooking produces the best onion flavor. Use broiler-safe bowls. Toast bread before topping so it holds up longer. Caramelized onions can be made ahead and refrigerated or frozen.