French Onion Soup (Soupe à l’Oignon Gratinée)

…in the slow cooker!french-onion-soup

It’s easy to make French onion soup. Did she say EASY? Yes, it can be easy, with a few simple steps and a slow cooker.

Let’s start with the onions. While most recipes state that onions cooked on the stove caramelize in 15 or even 25 minutes, you’re lucky if they are done in 45 minutes. Since caramelizing onions truly requires more time than many of us have for an average weeknight recipe, this method of “low and slow” caramelizing in the slow cooker over night will not only be a time saver, but will also produce a rich, deep savory flavor perfect for your soup starter. Add all the remaining ingredients to the slow cooker in the morning and go on with your day!

This recipe is for an onion soup without the thick crusted topping. But if that is your preference, see our Gr8 tip below. Delicieux!


French Onion Soup

Start this the night before you want to serve it because the onions caramelize in the slow cooker overnight!

Servings 6 servings
Author Jurga


  • 4 large yellow onions, thinly sliced
  • 4 Tablespoons butter, melted
  • 2 Tablespoons olive oil
  • 1 teaspoon salt
  • 1/4 teaspoon dried thyme
  • 2 cloves garlic, minced
  • 1/4 cup dry red wine or sherry
  • 1 Tablespoon balsamic vinegar
  • 4 cups low sodium beef stock, preferably homemade
  • 4 cups low sodium chicken stock, preferably homemade
  • Salt and pepper to taste
  • 4-6 slices French bread cut into 1 inch thick slices, toasted
  • 8-12 Tablespoons freshly grated Parmesan cheese
  • 8-12 Tablespoons freshly grated Gruyère (or Swiss) cheese


  1. Toss sliced onions with melted butter, oil and salt and place them in a lightly greased slow cooker.

  2. Cook on low and let the the onions caramelize over night, 10-12 hours.
  3. In the morning, throw in the thyme, minced garlic, red wine, balsamic vinegar, beef stock, chicken stock and S&P to taste.
  4. Cook on low for 8-10 hours.
  5. Preheat the oven broiler.
  6. Arrange the bread slices in a single layer on a baking sheet and broil 2 minutes, turning once until lightly toasted on both sides.
  7. Remove from the heat; do not turn off the broiler.
  8. Arrange oven-proof soup bowls on a rimmed baking sheet.
  9. Fill each bowl 2/3 full of soup.

  10. Place the toasted bread slices on top of the soup.
  11. Sprinkle the bread slices with 2 Tablespoons each of the Parmesan and Gruyère cheeses.

  12. Broil 5 minutes or until bread and cheese are golden brown.
  13. Serve immediately!

Recipe Notes

Gr8 Tips:

For a thick and beautifully melted crusted topping, use oven-safe crocks and thicker pieces of bread. Top each bowl with sliced (not shredded) Gruyère or Swiss cheese overlapping the slices onto the sides. Broil until the cheese softens and cascades over the side of the crock, about 5 minutes.

To get the very thinnest slices of onions, use a mandolin.



  1. Claudia Kerns | 13th Sep 15

    We love French onion soup!! This is so fantastic!! I can’t wait to try this. Working beyond full time makes cooking this type of dish during the week impossible. Do you have any recommendations for a store bought chicken and beef broth? Thank you!!

    • Jurga | 14th Sep 15

      Lon, I usually have homemade chicken stock in the freezer but when I use store bought I prefer Kitchen Basics chicken stock. Most of the other brands are either too salty or taste “fake”. Hope this helps!

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