Slow Cooker French Onion Soup

overhead of three bowls of french onion soup.

5 from 2 votes

This Crockpot French Onion Soup is a delicious and comforting. Serve as a light soup or top with bread and cheese for a heartier option!

Prep Time15

Servings: -6

Author: Lexi

Ingredients

3 tablespoons butter
1 tablespoon extra-virgin olive oil or avocado oil
4 white onions sliced
2 red onions sliced
1 tablespoon coconut sugar
3 cloves of garlic minced
1 teaspoon salt more to taste
1 teaspoon black pepper more to taste
1/4 cup balsamic vinegar
2 teaspoons dried thyme or 2 fresh thyme sprigs
2 bay leaves
7 cups beef broth
1/2 teaspoon fish sauce
1 tablespoon arrowroot flour
Optional: red pepper flakes for serving
Options: 1/4 cup shredded Gruyere cheese
Optional: 1/4 cup shredded mozzarella cheese
Optional: 1 batch bread see recipe here or here for nut-free

Instructions

Place butter and oil in the bottom of your slow cooker insert.
Add in sliced onions, coconut sugar, garlic, balsamic vinegar, half the salt and pepper, thyme and bay leaves. Toss to coat and cook on low for 6 hours.
After 6 hours, add in beef broth, fish sauce, arrowroot flour, and the remaining salt and pepper.
Let cook for the remaining 2 hours. Remove bay leaves and thyme sprigs if using fresh thyme. Taste and add salt and pepper as desired.
Heat the oven to 350°F. Divide the soup between oven-safe bowls. Top each with a slice (or two) of toasted bread and sprinkle cheese in a thick layer over the bread and up to the edge of the bowl. Bake for 20 to 30 minutes until cheese is bubbling. Broil on high for 1 minute.

Notes

To make in the Instant Pot:

Press the saute function on the Instant Pot. When hot place butter and oil in the pot along with the onions. Cook for 5 minutes, stirring once. Add in coconut sugar, garlic, balsamic vinegar, salt and pepper, thyme and bay leaves and cook on high pressure for 20 minutes. Once finished use the quick release function

Press cancel and remove the lid. If there is a lot of liquid in the bottom of the pot, press saute and cook until it has almost evaporated and the onions are a nice brown color and very jammy.

Add the arrowroot and stir until it has disappeared. Add in 4 cups of beef broth (this is different than the directions for the slow cooker) and fish sauce and close the lid and set to sealing. Finish cooking on manual high pressure, for 5 minutes. Use the quick release function. Season to taste. If topping the soup with bread and cheese follow the directions up above from step 5.

Nutrition