Easy Crock Pot French Onion Soup—Long and Slow

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.

Introduction

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.

🧅Ingredients

• 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.

❓FAQs

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This recipe is part of Our Best Soups.

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🖼️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.

📝Recipe

Editors Note: Originally published July 12, 2015. Updated with expanded options, refreshed photos, and a table of contents to help navigation.