French Onion Soup - Slow Cooker

Prep Time

15 minutes

Prep Notes

Who knew you didn’t need to slave over a stove for hours for French Onion Soup?

Cooking Time

8 hours


4 servings


  • 2 1/2 pounds red onions
  • 1/3 cup avocado oil or olive oil
  • 1/2 teaspoon kosher salt
  • A few peeled garlic cloves, optional
  • 4 cups low-sodium vegetable broth or beef broth
  • 2 beef bouillon cubes or 2 tablespoons beef bouillon granules
  • 1/3 cup full-bodied red wine, optional
  • Salt and black pepper, to taste
  • Croutons or crusty bread, for topping (I make my own croutons using gluten free bread)
  • Your favorite melty cheese ( SoDelicious Shreds ... they are new and pretty great!)

If you want more spices, try these after Step 5: 

2-3 tsp dried thyme
½ tsp black pepper
 large bay leaves
½ tsp garlic powder
½ tsp. onion powder


  1. Grease the interior of the slow cooker crock with nonstick cooking spray.
  2. Cut the onions in half on a cutting board, place them flat sides down, and cut them into 1/4-inch-thick slices. Place the slices in the crock. If they come almost to the top, don’t worry. They’ll sweat and shrink down.
  3. Pour the oil and spoon the salt over the onions. Add the garlic cloves, if desired. Stir. Cover. Cook on High for 6 hours.
  4. If you are home, stir up from the bottom after the first hour of cooking and again after another 2 hours. But if you’re away or cooking overnight, it’s not a problem.
  5. After 6 hours, make French Onion Soup by stirring in the broth, bouillon, and, if desired, wine. Proceed with Steps 6 through 8. Or season the onions with salt and pepper to taste, and then remove them to use in sandwiches or omelets.
  6. Cover. Continue cooking on High 1 to 2 more hours, or until the onions are tender. Remove the lid; cook 15 more minutes on High.
  7. Season to taste with salt and pepper.
  8. Serve in bowls. Top with the croutons or crusty bread and cheese, which will melt from the heat of the soup.


Make the onions overnight. They don’t need tending.

Follow the recipe through Step 5 for Caramelized Onions. Store them in the refrigerator for up to 3 days or freeze to use later. (Be sure to thaw frozen onions if proceeding to make soup.)

Make It Gluten-free: Use gluten-free bread or croutons.

Make It Vegetarian/Vegan: Substitute vegetable broth, preferably one with mushrooms, for the beef broth. Use a vegan cheese and sprinkle nutritional yeast on the bread.

Simple Swaps: Substitute leeks for half the onions. Switch up the toppings with different types of cheese.

Credit, Phyllis Good