Classic French onion soup features beefy broth loaded with caramelized onions, then topped with crusty bread and melted cheese. With only 10 minutes of preparation, you let your crock pot handle the all-day long low and slow cooking.
This elegant comfort food is as better as most restaurants, and you made it for pennies at home. Perfect for a small crock pot or double to make the family size.
Excellent onion soup is more than a beef broth with some onions. You need to get the caramelization going well, and that takes time. Let it cook all day to fully caramelize your onions for this soup's full depth of flavor.
French Onion Soup is from the 18th century; this traditional French soup can be used as an appetizer or a main course.
👨🍳How to make this recipe
- Trim 1 ½ pounds of onions (about 3 medium onions) into rings or petals.
- Add the onion to a 2 ½ quart or larger crock pot with butter and seasonings.
- Cook on high for 9 to 10 hours to caramelize. This is variable, depending on your crock pot. Check early several times. Please see the section on crock pots below.
- Add beef broth and cook one more hour on high.
- Serve usually with toasted crusty bread and topped with cheese browned under a broiler.
- Onions—Regular yellow or white onions are the best choices, but some red onions can be mixed in. Some prefer sweet onions like Vidalias, Mauis, and Walla Wallas to add sweetness.
- Beef Broth—Very few commercial beef broths or stocks are above adequate, and many are just bad. I suggest Swanson®️ broth or stock or use one you know. You can also do homemade stock or broth. Vegetable broth can be used.
- Seasoning—The seasoning is limited to some dry or fresh thyme with salt and pepper. One to two cloves of garlic can be added with the onions.
- Worcestershire sauce—will make the "beef" flavor pop and add more flavor. It can be used in many cooking applications to boost that beef test, especially beef broth. I'm using Lee and Perrins Worcestershire Sauce, which I trust, but I suspect there are other good choices.
- Cheese—gruyere, provolone, or Swiss cheese are preferred. But even mozzarella cheese will work.
- Crusty bread or croutons—toast a buttered slice of French bread on a baking sheet in the oven. Large croutons can also be used.
Note on ingredient quality: 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.
Caramelizing onions in a crock pot
Caramelization is the browning of sugar through the oxidation of those sugars. It results in a deep nutty flavor and brown color when correctly done. 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 9-10 hours, but this may be a few hours less or more depending on your crock pot.
♨️About the crock pot
This recipe fits well in a small crock pot of 2 quarts minimum. Double recipes (what I suggest making) need 4 quarts or bigger.
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 acceptable but may cook a bit faster.
Troubleshooting 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 about crock pots and their temperatures.
On a crock pot, the maximum temperature on both low and high should be 212° range, but it will take different times 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. If your crock pot boils on low, it may be in the "runs hot" category, then use low for this recipe.
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.
A few readers have had burnt onions, but 9-10 hours on high consistent with other similar recipes and less than American Test Kitchen (subscription required), which is 10-12 hours on high.
For the cheese, we like provolone, but some prefer gruyere or Swiss cheese. I like to use slices of cheese, but shredded cheese works fine. Again, quality matters.
You can use what you want, but I choose a nice crusty French baguette.
Some crusty bread or large croutons are used to float cheese on top. You can skip it, but it is traditional and helps keep the cheese on top.
Store in an airtight container. Good refrigerated for 3-4 days and 3-4 months frozen.
Wine is not required for onion soup. It has traditionally been used to de-glaze the pan after caramelizing the onions—not needed with a crock pot. But the wine also added flavor to the soup.
Never cook with 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.
📖Crock Pot Soups
This recipe is part of Our Best Soups.
This recipe is listed in these categories. See them for more similar recipes.
🖼️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 petals—add to a 2 ½ quart or larger crock pot. 4 quarts or a larger crock pot are needed if doubling the recipe. Triple needs larger than 6 quarts.
Add 1 teaspoon of coarse salt, 2 tablespoons of butter, ½ teaspoon of black pepper, 1 ½ teaspoon Worcestershire sauce, and ½ teaspoon of thyme. Then stir them together. The butter can go in unmelted, but you must stir in 1 hour or melt it in the microwave.
Cook on high for 9-10 hours with lid on until nicely darker brown. Be warned that some crock pots may run hot, and please watch for the endpoint of "softened and deep golden brown" for the onions being done, and don't go by time alone. Then add 4 cups of beef broth and cook on high for at least one hour.
Preheat the broiler to high. Arrange ramekin or oven-safe bowls on a cookie sheet. Ladle hot soup into the bowls, and float toasted crusty bread on the soup.
Cover each bowl with the cheese of your choice.
Broil until cheese is bubbly and golden, 2-4 minutes.
Easy Crock Pot French Onion Soup—Long and Slow
- 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
- ½ cup Wine - optional
Finishing then serving
- Crusty bread
- Cheese of choice for topping
- Chop 1 ½ pounds of onions, about 3 medium size onions. Some people will want rings or petals—add to a 2 ½ quart or larger crock pot. 4 quarts or a larger crock pot are needed if doubling the recipe. Triple needs larger than 6 quarts.
- Add 1 teaspoon of coarse salt, 2 tablespoons of butter, ½ teaspoon of black pepper, 1 ½ teaspoon Worcestershire sauce, and ½ teaspoon of thyme. Then stir them together. The butter can go in unmelted, but you must stir in 1 hour or melt it in the microwave.
- Cook on high with lid on for 9-10 hours until nicely darker brown. Be warned that some crock pots may run hot, and please watch for the endpoint of "softened and deep golden brown" for the onions being done, and don't go by time alone. Then add 4 cups of beef broth and cook on high for at least one hour. Toast slices of crusty bread·butter, and bake.
- Preheat the broiler to high. Arrange ramekin or oven-safe bowls on a cookie sheet. Ladle hot soup into the bowls, and 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.
Your Own 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 doubled 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.