Classic French onion soup features beefy broth loaded with caramelized onions topped with crusty bread and melted cheese. Elegant comfort food made ridiculously easy with your slow cooker. Perfect for a small crock pot or double to make the family size.
Better than restaurant quality, this crock pot French Onion Soup is perfect for everyday or special meals.
I love good French onion soup. I mean really love it. If it's on the menu, I usually make sure I have it.
Unfortunately, that means the good, the bad, and the ugly. I should put adequate on that list too. I can live with adequate, but most seem to be wanting and falling into the bad/ugly range.
Very nice solid lower 5. You can make a little better French onion soup but with a lot more work. This is much better than most restaurants. I have had only a few better.
What is French Onion Soup?
From the 18th century, this traditional French soup can be used as an appetizer. But I love a bigger bowl for the main course.
Good onion soup is more than a beef broth with some onions. You need to get the caramelization going well, or you have nothing. You need some long cooking to get there.
Caramelization is the browning of sugar through the oxidation of those sugars. When correctly done, it results in a deep nutty flavor and brown color. Just what we need for a great soup
While many techniques require multiple rounds of caramelization on the stovetop, you can do it in a crock pot. I'm lazy... I pick number two.
Start by loading a slow cooker with some chopped-up onions. Cook with butter, salt, pepper, and thyme. Add a little Worcestershire sauce to deepen the flavor. Cook on high for a long time, add the broth and cook a little longer. Then serve your favorite way. Yum...
📋Ingredients for French Onion Soup
With many other recipes, you can use cheaper generic ingredients and get away with it. But with so few ingredients, quality matters here. So only use ingredients you trust.
Regular yellow or white onions are best. I consider white and red onions equivalent to my usual yellow onions, and some people like a mix.
Sweet onions like Vidalias, Mauis, Walla Wallas are probably not a good idea here. I don't like much sweetness here, and that may spoil the broth. But some people prefer the sweetness of these onions and may even add sugar, so your choice.
Very few commercial beef broths or stocks are above adequate, and many are just bad.
I like Swanson broth. I think it has improved in quality over the years and is quite good now. The Swanson stock is also good, but I detect no difference in use, so I don't spend the extra money.
You can do home stock or broth. It is easy to make and store but is not this recipe. It seems a little the top for a crock pot soup.
Worcestershire sauce will make the "beef" flavor really pop. It can be used in many cooking applications to boost that beef test, especially when using beef broth.
I'm using Lee and Perrins Worcestershire Sauce, which I trust, but I suspect there are other good choices.
For the cheese, we like provolone, but some prefer gruyere or Swiss cheese. I like to use slices of cheese, but shredded workes fine.
Again, quality matters.
You can use what you want, but a nice crusty French baguette is my choice.
Some crusty bread is used to float cheese on top. You can skip it, but it is traditional and helps keep the cheese on top.
The bread must be toasted to prevent a sloppy mess. I use thinner slices, but many like cubes of bread, more like large croutons.
Wine is not required for onion soup.
Wine has traditionally been used to de-glaze the pan after caramelizing the onions—not really needed with a crock pot. But the wine also added flavor to the soup.
Never cook with a wine you don't like. While I can enjoy food cooked with wine, it is not a taste I need in the food. I prefer mine in a glass.
If you are using a wine (an option in the tips of the recipe card), I suggest a non-sweet, dry white, or red wine. A few suggestions: Sauv Blanc, Semillon, Pinot Grigio, Chardonnay, Merlot or Pinot Noir.
♨️What Crock Pot to Use for Onion Soup
This recipe can be easily double but could also be cut in half. The volume of this recipe is about 6 cups. Slow cookers should not be overfilled, which means more than 75% full. Most feel that bigger is fine but may cook a bit faster.
So this fits well in a small crock pot of 2 quarts minimum. Double recipes (what I suggest making) need 4 quarts or bigger.
Trouble shooting crock pot temperature
Several readers have had trouble with 9 hours on high "burning." Whether they are interpreting deep caramelization for burning or they are really burnt, I can't say, but let's talk crock pots and their temperatures a bit.
On a crock pot, both low and high should be 212° range and take a different time to get there. That is all controlled by a thermostat that has improved over the years.
Some crock pots (especially older ones) can run over 300°, which may be the issue. Also, even newer crock pots can have a malfunctioning thermostat.
So be advised that some crock pots may run hotter, so watch for "softened and deep golden brown" as the endpoint for the onions being done. I would say if your crock pot boils on low, it may be in the "runs hot" category, then use low for this recipe.
One other note, if you are using a full-size crock pot for this smaller recipe, you have less material to heat, and it may cook a bit faster. So right size crock pot is important, or watch the endpoint carefully.
My 9-10 hours on high stands and is consistent with other similar recipes and less than Cooks Illustrated, which is 10-12 hours on high.
Storage of French Onion Soup
Store in an airtight container. Good refrigerated for 3-4 days and 3-4 months frozen.
📖Crock Pot Soups
This recipe is part of Our Best Soups.
🖼️Step-by-Step Photo Instructions
Start with simple ingredients. The butter may be with or without salt.
Chop 1 ½ pounds of onions about 3 medium size onions. Some people will want rings or some petals—add to a 2 ½ quart or larger crock pot. If doubling the recipe, a 4 quarts or larger crock pot is needed. Triple needs larger than 6-quarts.
Add one teaspoon coarse salt, two tablespoons of butter, ½ teaspoon pepper, 1 ½ teaspoon Worcestershire sauce, and ½ teaspoon thyme. The butter can go in unmelted, but you will need to stir in 1 hour or melt it first in the microwave.
Cook on high for 9-10 hours until nicely darker brown. Be warned that some crock pots may run hot, and please watch for the endpoint and don't go by time alone. Using a larger crock pot may also lead to cooking too rapidly. Then add 4 cups of beef broth and cook on high for at least one hour more.
Preheat broiler to high. Arrange ramekin or oven-safe bowls on a cookie sheet. Ladle hot soup into the bowls, float toasted crusty bread on the soup.
Cover each bowl with cheese of your choice.
Broil until cheese is bubbly and golden, 2-4 minutes.
Crock Pot French Onion Soup
- 1 ½ pounds onions - about 3 medium size onions
- 1 teaspoon coarse salt
- 2 tablespoons butter
- ½ teaspoon pepper
- 1 ½ teaspoon Worcestershire sauce
- ½ teaspoon thyme
- 4 cups beef broth
- Crusty bread
- Cheese of choice for topping
- ½ cup Wine - optional
- Chop 1 ½ pounds of onions about 3 medium size onions. Some people will want rings or some petals—add to a 2 ½ quart or larger crock pot. If doubling the recipe, a 4 quarts or larger crock pot is needed. Triple needs larger than 6-quarts.
- Add one teaspoon coarse salt, two tablespoons butter, ½ teaspoon pepper, 1 ½ teaspoon Worcestershire sauce and ½ teaspoon thyme. The butter can go in unmelted, but you will need to stir in 1 hour or melt it first in the microwave.
- Cook on high for 9-10 hours until nicely darker brown. Be warned that some crock pots may run hot and please watch for the endpoint and don't go by time alone. Then add 4 cups of beef broth and cook on high for at least one hour more.
- Preheat broiler to high. Arrange ramekin or oven-safe bowls on a cookie sheet. Ladle hot soup into the bowls, float toasted crusty bread on sou
- Cover each bowl with cheese of your choice.
- Broil until cheese is bubbly and golden, 2-4 minutes.
My Private Notes
- Be advised that some crock pots may run hotter so watch for softened and deep golden brown as the endpoint for the onions being done. I would say if your crock pot ever boils on low, it may be in the "runs hot" category, then use low for this recipe. More discussion in the post.
- Also, using a much larger crock pot for this small recipe may cook a bit faster.
- Please check the onions halfway through due to the above.
- This recipe can be easily double but could also be cut in half.
- This makes about 6 cups of soup. I call that 4 servings of 1 ½ cups each.
- As written, use a 2 ½ to 4-quart crock pot. For a double recipe, you will need 4-quart or more. A triple recipe fits in a 6 quart or larger.
- Some type of crusty bread is used to float cheese on top. You can use what you want, but a nice crusty French baguette is my choice. For the cheese we like provolone, but some prefer Gruyere or Swiss.
- Quality matters here in the choice of broth. Do not cheap out on generic.
- Wine can be added to the soup with the broth. A half cup would be about the right amount. Suggestions discussed in the post.
- Good refrigerated for 3-4 days and 3-4 months frozen.
To adjust the recipe size:
You may adjust the number of servings in this recipe card under servings. This does the math for the ingredients for you. BUT it does NOT adjust the text of the instructions. So you need to do that yourself.
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Editors Note: Originally published July 12, 2015. Updated with expanded options, refreshed photos, and a table of contents to help navigation.