Slow Cooker French Onion Soup

No more standing over the stove, make French Onion Soup in the Slow Cooker. Let the crockpot do all the hard work, with minimal prep work you can now have this classic French soup at home with ease!

This post may contain Affiliate Links.

How To Make French Onion Soup in the Slow Cooker

Made famous by Julia Child, French Onion Soup has become synonymous with ordering at a restaurant or standing over the stove top for what seems to be an hour.

Until now with the helpful use of the slow cooker…

Making French Onion Soup in a slow cooker is extremely easy and hands off. The catch is that it can take a while… like about 24 hours to make the soup. But it is so hands off it makes it easy!

French Onion Soup done in the crockpot is done in three steps. 

The first step is to make caramelized onions in the crockpot (I have a whole post you can look at that specifically talks about how to make caramelized onions in the slow cooker here). After you make the caramelized onions in the crockpot you’ll make the soup portion. Add broth and flavorings and let the soup simmer. Then it is time to go onto the third step.

Lastly the soup will need to be prepared for serving. The soup will be poured into ramekins or oven safe bowls then topped with little toasts and sprinkled with cheese.

The soup will then be baked in the oven to get that nice cheesy top with the toast that you know is everyone’s favorite part!

Ingredients

• Onions – Onions are the key to French Onion Soup, if that isn’t already obvious. For this recipe we will use yellow onions to get the correct flavor of French Onion Soup. The onions should be measured by weight opposed to how many to get the correct amount. So 3 pounds, but if you don’t have a scale it is usually four medium to large onions.
• Butter – Butter is used to make the caramelized onion, giving those onions the texture and golden brown color. Use unsalted butter because we will be adding our own salt and you don’t want onions to be overly salty.
• Olive Oil – Olive oil will also be used to make the caramelized onions. This will help keep them smooth and silky while they cook.
• Salt – You will use most if not all of the salt in the dish during the caramelized onion portion. You’ll use quite a bit and it is best to use either kosher salt or sea salt. If you are in a pinch and only have table salt available, use half of the amount and you can always check the saltiness of the dish later.
• Black Pepper – This is optional but if you want to give your caramelized onions, a little bit of a pizzazz, feel free to add some freshly ground black pepper to the caramelized onions.
• Beef Broth – The beef broth is the other large component of the soup. It is obviously going to be best to use a homemade beef broth or stock but since that is an always an option, try to buy a nicer brand at the grocery store. Since there aren’t a lot of ingredients in the soup, a lot of the flavor will come from the beef broth that you buy. Another thing to note when buying beef broth is to look for a reduced sodium version so that your soup isn’t too salty. At the store look for a broth that says either low sodium or 50% less sodium. In a pinch I would even rather grab a no salt beef broth and add your own salt to keep your soup from becoming too salty.
• Balsamic Vinegar – Just a little bit of balsamic to add a nice flavor to the soup.
• Brandy/Cognac – Most people consider this a must for the soup. It really adds a good flavor. If your family is not a drinking family you can leave it out, consider it optional. And don’t worry about the alcohol content, you add it before it cooks so all the alcohol will cook out before serving.

For a complete detailed list of the ingredients continue towards the bottom of the page.

instructions

Add the onions, olive oil, butter, salt, and pepper (if using) to the crockpot. Cook on low for about 14 hours. Stirring 2-3 times if available.

Once the onions are caramelized you are ready to start the soup. Add the beef broth, balsamic vinegar, and cognac. Stir and cook on low about 7-8 hours.

To prepare for serving. Preheat the oven to 425° F. Cut the baguette into 1 inch slices, 2-3 for each bowl (depending on the size). Place on a sheet pan and bake for about 7-8 minutes until the bread is toasty.

Fill the soup into the bowls. Dunk and arrange on top 2-3 toasts per bowl. Top with 1/3 cup of the cheese. Place the bowls on a sheet pan for ease. Transfer to the oven. Cook about 10 minutes until cheese is nice and gooey. Be cautious when serving, the bowls are hot.

And make sure you are following me on TikTok, Instagram, and Pinterest, for all the latest recipes!