Slow Cooker French Onion Soup is made with caramelized onions & beef broth for a flavorful savory soup. French Onion Soup made easy in the crockpot for a simple & satisfying dinner!
Serve this Crockpot French Onion Soup with a toasted slice of baguette bread with melted cheese on top, it is comfort in a bowl! It is one of the Best French Onion Soup recipes for the colder months ever created, in my opinion. It is rich in flavor thanks to the caramelization of the onions in combination with the beef stock. With a subtle hint of earthy herbs like thyme. Think about it, coming home on a cold day and having ready for you a comforting bowl of this delicious French Onion soup. This is an absolute must-try for the Winter season!
What is traditional French Onion Soup?
There are many versions of this wonderful soup recipe across European cuisines, however, the classic French Soup is the most famous one. Classic French Onion Soup is made with beef broth and includes some type of alcohol like Cognac or Brandy. Other versions might include chicken stock instead of beef stock and white wine, and some do not include any alcohol. Do not worry, including a bit of an alcoholic drink in it is absolutely safe, even for kids, since the majority of the alcohol will evaporate while cooking.
Classic French soup has thyme and bay leaves as the herbs of choice while other versions use sage and rosemary. Also, it is topped up with good quality baguette bread with melted Gruyere and Emmental with the occasional appearance of other cheeses like Parmesan (although not traditional).
What type of onions should you use for French Onion Soup?
Although is possible to make it with any type of onion (believe me I’ve tried it!) my personal recommendation is to make it with yellow onions or sweet white onions like Vidalia onions. They give the soup a fantastic flavor and the texture is just right using these types of onions.
How do I get perfect Caramelized Onions?
The key step for this delicious soup is the proper caramelization of the onions. I am speaking about the long and steady process where onions become translucent and golden brown with the caramelization of their natural sugars, so no, we are not going to use any sugar in this recipe.
Caramelization starts with cutting all the onions in same-sized pieces, so they cook evenly. The best is to slice them thinly so they can cook a bit quicker. Then follows the melting of a couple of tablespoons of butter and cooking the onions on slow heat with a bit of salt so they release their juices. Keep stirring every now and then and let them do their thing on very low heat (that is key!) so they do not burn. There is nothing worse than burned onions for your soup, well, yeah maybe undercooked onions are equally bad in this recipe.
The key step is to make the onions “sweat” slowly, stirring occasionally until they achieve its golden translucent perfection, and for this, it requires time. Depending on your pan size and the number of onions you have used, it might take something from 45 mins to 1 hour. I am sorry there is no shortcut for this step, but it will be worth if for the final results!
Ingredients for Slow Cooker French Onion Soup
As I have already given some hints on the ingredients, here is the full details of ingredients that are needed for this Classic French Onion soup:
–Onions: Use 5-6 large yellow onions, as said before use yellow onions or sweet white like Vidalia onions if possible.
–Butter: You need 4 tablespoons butter to help caramelize the onions. Butter gives the best results flavor wise, so don’t skip it or substitute it with any cooking oil.
–Brandy or cognac: Using ½ cup brandy or cognac to add richness to the caramelized onions, as said do not worry about the alcohol content since it will be evaporated while cooking. You can also use white wine instead of Brandy or cognac, however, it can give an acidic aftertaste, so I prefer to use the first options instead.
–Beef stock: You need 6 cups of beef stock, homemade if possible for best results. However store-bought (low sodium) is also a good option if you don not have homemade stock ready to use.
–Flour: Using 3 tablespoons white flour will help to thicken the soup.
–Herbs: You will need 2 bay leaves and 4 sprigs of fresh Thyme or 1 teaspoon dried, plus a little more for the final garnish. Try to avoid using Rosemary since it is an overpowering taste and may alter the recipe results.
–Salt & Pepper: Salt and pepper to taste, add a small amount of each at a time and consider doing this step when you are ready to eat.
–Bread: You will need 1-2 slices of baguette bread per bowl for the best results. Feel free to use the bread of your choice, just make sure it is a bread that can hold together well after being submerged in soup.
–Grated Cheese: The popular choices of cheese are Swiss, Gruyere, Gouda, Parmesan or Mozzarella. You can use almost any cheese that melts well, Parmesan makes for a great topping to the soup.
–Worcestershire Sauce: This is an optional ingredient, feel free to add it to your soup, but I personally don’t find it necessary.
Step by step instructions for how to make Slow Cooker French Onion Soup
Preparing onions and beef broth
First step is the Caramelization of the onions! Start by slicing the onions thinly, the thinner the better so they cook a bit faster. Yes, you are going to cry a lot!
In a large pan on medium heat, add the butter and melt.
Then, add the sliced onions and let cook for 1 minute or so before you stir them.
Next, add a little bit of salt to the onions and mix well, turn to low heat and keep stirring every 5 minutes or so.
When you start to see the onions browning, add a splash of the cognac to deglaze and keep cooking until all the onions are translucent and a soft golden brown.
After than, add the flour and cook it for 1-2 minutes or so, stirring constantly to avoid it from burning.
Then, add a splash of the beef stock and dilute the flour in it and mix well to combine.
Once the flour has mixed well and completely dissolved, transfer the caramelized onions from the pan to the slow cooker.
Continue to add the rest of the beef stock and herbs to the slow cooker and mix well.
Slow Cooker cooking information
Set on low heat and let cook for 5-6 hours.
Towards the last 30 minutes, carefully taste the soup and add the salt and pepper as desired.
Preparing the bread and putting together the final dish
Preheat the oven to 400º F. Slice the baguette bread, place on baking sheet and toast bread for 5-7 minutes.
In oven safe soup bowls power the onion and broth mixture into each bowl, top each bowl with 2 slices of bread and add some grated cheese on top.
Change oven setting to broil.
Place the full soup bowls in the oven and broil for 8-10 minutes. Be very careful when removing from the oven!
Step by step instructions for Stovetop method
Preparing onions and beef broth
First step is the Caramelization of the onions! Start by slicing the onions thinly, the thinner the better so they cook a bit faster. Yes, you are going to cry a lot!
In a Dutch oven on medium heat, add the butter and melt. If you do not have a Dutch oven, a large pot will also do.
Then, add the sliced onions and let cook for 1 minute or so before you stir them.
Next, add a little bit of salt to the onions and mix well, turn to low heat and keep stirring every 5 minutes or so.
When you start to see the onions browning, add a splash of the cognac to deglaze and keep cooking until all the onions are translucent and a soft golden brown.
After than, add the flour and cook it for 1-2 minutes or so, stirring constantly to avoid it from burning.
Then, add a splash of the beef stock and dilute the flour in it and mix well to combine.
Continue to add the rest of the beef stock and herbs to the pot and mix well.
Cooking information
Set on low heat and let cook for 5-6 hours.
Towards the last 30 minutes, carefully taste the soup and add the salt and pepper as desired.
Once it has simmered for 2-3 hours, remove it from heat.
Preparing the bread and putting together the final dish
Preheat the oven to 400º F. Slice the baguette bread, place on baking sheet and toast bread for 5-7 minutes.
In oven safe soup bowls power the onion and broth mixture into each bowl, top each bowl with 2 slices of bread and add some grated cheese on top.
Change oven setting to broil.
Place the full soup bowls in the oven and broil for 8-10 minutes. Be very careful when removing from the oven!
Slow Cooker French Onion Soup
Ingredients
- 5-6 large yellow onions
- 4 tablespoons butter
- 3 tablespoons white flour
- ½ cup brandy or cognac
- 6 cups of beef stock
- 2 bay leaves
- 4 sprigs of fresh thyme or 1 teaspoon dried)+ some more for the final garnish
- Salt and pepper to taste
- Baguette bread one or two slices per bowl of soup
- 1 cup Grated cheese: Swiss or Gruyere Gouda, Parmesano or Mozzarella
Instructions
Step by step instructions for how to make Slow Cooker French Onion Soup
- First step is the Caramelization of the onions! Start by slicing the onions thinly, the thinner the better so they cook a bit faster.
- In a large pan on medium heat, add the butter and melt.
- Then, add the sliced onions and let cook for 1 minute or so before you stir them.
- Next, add a little bit of salt to the onions and mix well, turn to low heat and keep stirring every 5 minutes or so.
- When you start to see the onions browning, add a splash of the cognac to deglaze and keep cooking until all the onions are translucent and a soft golden brown.
- After than, add the flour and cook it for 1-2 minutes or so, stirring constantly to avoid it from burning. Then, add a splash of the beef stock and dilute the flour in it and mix well to combine.
- Once the flour has mixed well and completely dissolved, transfer the caramelized onions from the pan to the slow cooker.
- Continue to add the rest of the beef stock and herbs to the slow cooker and mix well.
- Set on low heat and let cook for 5-6hours.
- Towards the last 30 minutes, carefully taste the soup and add the salt and pepper as desired.
Preparing the bread and putting together the final dish
- Preheat the oven to 400º F. Slice the baguette bread, place on baking sheet and toast bread for 5-7 minutes.
- In oven safe soup bowls power the onion and broth mixture into each bowl, top each bowl with 2 slices of bread and add some grated cheese on top.
- Change oven setting to broil.
- Place the full soup bowls in the oven and broil for 8-10 minutes. Be very careful when removing from the oven!
Step by step instructions for Stovetop method
- First step is the Caramelization of the onions! Start by slicing the onions thinly, the thinner the better so they cook a bit faster. Yes, you are going to cry a lot!
- In a Dutch oven on medium heat, add the butter and melt. If you do not have a Dutch oven, a large pot will also do.
- Then, add the sliced onions and let cook for 1 minute or so before you stir them.
- Next, add a little bit of salt to the onions and mix well, turn to low heat and keep stirring every 5 minutes or so.
- When you start to see the onions browning, add a splash of the cognac to deglaze and keep cooking until all the onions are translucent and a soft golden brown.
- After than, add the flour and cook it for 1-2 minutes or so, stirring constantly to avoid it from burning.
- Then, add a splash of the beef stock and dilute the flour in it and mix well to combine.
- Continue to add the rest of the beef stock and herbs to the pot and mix well.
- Set on low heat and let cook for 5-6hours. Towards the last 30 minutes, carefully taste the soup and add the salt and pepper as desired.
- Once it has simmered for 2-3 hours, remove it from heat.
- Follow the same instructions for Preparing the bread and final dish
Notes
Nutrition
📫 Save this recipe! Send it to your email! 📩
I consent to receiving emails from this site.
How do I make this recipe if I do not have oven safe bowls?
If you find yourself craving this savory soup but you do not have oven-safe bowls, we’ve got you covered! Prepare everything the same except you add the cheese to the bread BEFORE you broil it. This way your cheese is melted and your bread is toasted, then add the cheesy bread to the bowl of onion and broth soup.
Can I make this a vegetarian or vegan soup?
You can make this soup vegetarian or vegan by substituting the butter with olive oil and using vegetable broth instead of beef broth. Add vegan cheese or skip it entirely, however, that would result in a bit of a sad soup. There are so many great alternative options these days, you do not have to miss out due to dietary restrictions anymore!
How long will this French Onion Soup last?
It can be stored in the fridge for up to 6 days in an air-tight container, obviously, without the toasted bread + cheese on top. When you are ready to enjoy, toast your bread and melt your cheese!
Linda Gail Krupp says
Turned out great tasted as good if not better than a restaurant French Onion Soup. I used a mix of Swiss cheese and Mozzarella.
Nicole says
Thanks so much for sharing, we’re glad you liked it. That cheese combination sounds delicious!
Mike says
Ref: “Once it has simmered for 2-3 hours, remove it from heat.” Could you please explain this step? It seems out of place.
Jessica says
Agreed! I adapted this from a stovetop recipe. I omitted that step. 🙂