I love preparing my French Onion Soup Recipe with a blend of elegance and simplicity. Sautéing thinly sliced yellow onions in unsalted butter and olive oil before adding minced garlic and dry white wine creates a subtle, enticing aroma. Combined with rich beef broth and hints of thyme, every element sings with character.

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I recently tried this Slow Cooker French Onion Soup and it blew my mind. I mix 6 large yellow onions, thinly sliced, with 3 tablespoons unsalted butter, 1 tablespoon olive oil, a teaspoon of salt plus a pinch extra, and 1/4 teaspoon granulated sugar.

Then, I toss in 2 cloves of garlic, minced, and 1/2 cup of dry white wine to really get that rich flavor going. After that, I add 8 cups of low sodium beef broth along with a bay leaf and 1/4 teaspoon dried thyme (or if you prefer, 2 teaspoons fresh thyme leaves).

It all comes together in my crock pot slow cooker so that I can just set it and forget it. The best part is topping it off with a couple of toasted French baguette slices and 2 cups of grated Gruyere cheese.

Honestly, this soup is one of the best and easiest onion soup recipes out there, and it’s a total game changer for any slow cooker soup experiment.

Why I Like this Recipe

1. I love how easy it is to make. Since the recipe is practically hands-off in a slow cooker, I don’t have to worry much about stirring or timing every step which makes my busy days so much less stressful.

2. I enjoy the deep, caramelized flavor that comes from slowly cooking the onions. Even though it takes hours, I know the reward is a rich, sweet taste that always reminds me of home-cooked meals.

3. I like the combination of textures in the soup. The crunchy toasted baguette topped with melty Gruyere creates a mix of flavors and crunchiness that makes the dish extra satisfying.

4. I appreciate how forgiving this recipe is. Even if I mess up a little with the seasoning or timing, it’s still comforting and delicious which makes it a perfect go-to meal whenever I’m feeling a bit lazy.

Ingredients

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Yellow onions are fiber-rich and turn sweet when slowly caramelized, addin flavor and body.
Unsalted butter brings creamy fat tones and richness that help meld the soup’s flavors.
Dry white wine adds tangy acidity and eases bitterness, brightenin the overall profile.
Beef broth is savory and protein-packed; its hearty base gives depth to the dish.
Gruyere cheese offers a nutty, melty finish along with a boost of protein and calcium.

Ingredient Quantities

6 large yellow onions, thinly sliced

3 tablespoons unsalted butter

1 tablespoon olive oil

1 teaspoon salt, plus extra to taste

1/4 teaspoon granulated sugar

2 cloves garlic, minced

1/2 cup dry white wine

8 cups beef broth (preferably low sodium)

1 bay leaf

1/4 teaspoon dried thyme or 2 teaspoons fresh thyme leaves

Freshly ground black pepper, to taste

4-6 slices French baguette, toasted

2 cups grated Gruyere cheese

How to Make this

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1. Add the thinly sliced onions to your slow cooker along with the butter, olive oil, salt, and sugar and give it a good stir so everything is coated well.

2. Toss in the minced garlic and mix it in with the onions.

3. Slowly pour the dry white wine over the onions and garlic making sure it blends in nicely.

4. Pour in the beef broth then add the bay leaf and thyme, and finish with a few grinds of black pepper.

5. Cover the slow cooker and let everything cook on low for about 8 hours or on high for around 4 hours until the onions are deeply caramelized.

6. When the cooking time is nearly up, check the soup and remove the bay leaf, then adjust with extra salt and pepper if needed.

7. Preheat your broiler while the soup is finishing up so that it’ll be ready in a minute.

8. Ladle the hot soup into ovenproof bowls and carefully place a toasted slice of French baguette on top of each bowl.

9. Liberally sprinkle the grated Gruyere cheese over the baguette slices, making sure not to skimp on the good stuff.

10. Pop the bowls under the broiler for 3 to 5 minutes, just until the cheese is bubbly and golden, then carefully take them out and serve immediately.

Equipment Needed

1. A slow cooker
2. A cutting board and a sharp knife for slicing the onions and mincing the garlic
3. Measuring cups and spoons to accurately measure butter, olive oil, salt, sugar and wine
4. A large mixing spoon to stir your ingredients in the slow cooker
5. A ladle for transferring the soup into bowls
6. Broiler-safe ovenproof bowls for assembling the soup with the toasted baguette and cheese
7. An oven with a broiler setting to melt and brown the Gruyere cheese
8. A cheese grater if your Gruyere isn’t already pre-grated

FAQ

Can i use a different broth than beef broth?

Sure you can use vegetable broth if you prefer, but the soup might not have the same rich flavor you get from beef broth.

Do i have to cook the onions for a really long time?

Yeah, letting them cook slowly for about 8 hours on low helps them become super soft and caramelized which is key for that deep flavor.

Can this recipe be prepped ahead of time?

Definitely, you can chop the onions and measure out the ingredients the night before and just dump everything in the slow cooker in the morning.

What if my soup turns out too salty?

If it gets too salty, add a little extra water or more low sodium broth to balance it out.

Any tips for melting the Gruyere cheese on top?

Toast your French baguette slices, top them with the cheese, and pop them under the broiler for a couple of minutes until the cheese is all melted and bubbly.

Slow Cooker French Onion Soup Recipe Substitutions and Variations

If ya dont have yellow onions, try using red or white onions for a bit of a twist.
You can use salted butter instead of unsalted butter, just remember to cut back on extra salt later.
No dry white wine? You could use dry vermouth or a mix of white grape juice with a splash of vinegar instead.
If beef broth isn’t available, chicken or even veggie broth works alright in a pinch.
Can’t find Gruyere cheese? Swiss cheese makes for a good substitute and still gives you a tasty finish.

Pro Tips

1. When you’re caramelizing them onions, make sure you let ’em cook real slow and low so they really deepen in flavor. If you’re in a rush and bump up the heat, you might end up with burnt bits instead of that sweet, rich taste you’re lookin for.
2. Keep a close eye on the seasoning as you go along – every slow cooker can act a little different. Taste it a couple times over the cooking time and don’t be afraid to add a pinch more salt or pepper at the end.
3. When you’re under the broiler with those cheesy baguettes, be careful not to walk away. The cheese can go from bubbly to burnt really fast if you’re not watching it.
4. Use quality beef broth and real butter – it may seem small but these choices really boost the overall flavor, giving your soup that extra depth that makes it stand out.

Slow Cooker French Onion Soup Recipe

Recipe by Francis Mead

0.0 from 0 votes

Servings

servings

Calories

450

kcal

Equipment: 1. A slow cooker
2. A cutting board and a sharp knife for slicing the onions and mincing the garlic
3. Measuring cups and spoons to accurately measure butter, olive oil, salt, sugar and wine
4. A large mixing spoon to stir your ingredients in the slow cooker
5. A ladle for transferring the soup into bowls
6. Broiler-safe ovenproof bowls for assembling the soup with the toasted baguette and cheese
7. An oven with a broiler setting to melt and brown the Gruyere cheese
8. A cheese grater if your Gruyere isn’t already pre-grated

Ingredients

6 large yellow onions, thinly sliced
3 tablespoons unsalted butter
1 tablespoon olive oil
1 teaspoon salt, plus extra to taste
1/4 teaspoon granulated sugar
2 cloves garlic, minced
1/2 cup dry white wine
8 cups beef broth (preferably low sodium)
1 bay leaf
1/4 teaspoon dried thyme or 2 teaspoons fresh thyme leaves
Freshly ground black pepper, to taste
4-6 slices French baguette, toasted
2 cups grated Gruyere cheese

Directions

Add the thinly sliced onions to your slow cooker along with the butter, olive oil, salt, and sugar and give it a good stir so everything is coated well.
Toss in the minced garlic and mix it in with the onions.
Slowly pour the dry white wine over the onions and garlic making sure it blends in nicely.
Pour in the beef broth then add the bay leaf and thyme, and finish with a few grinds of black pepper.
Cover the slow cooker and let everything cook on low for about 8 hours or on high for around 4 hours until the onions are deeply caramelized.
When the cooking time is nearly up, check the soup and remove the bay leaf, then adjust with extra salt and pepper if needed.
Preheat your broiler while the soup is finishing up so that it’ll be ready in a minute.
Ladle the hot soup into ovenproof bowls and carefully place a toasted slice of French baguette on top of each bowl.
Liberally sprinkle the grated Gruyere cheese over the baguette slices, making sure not to skimp on the good stuff.
Pop the bowls under the broiler for 3 to 5 minutes, just until the cheese is bubbly and golden, then carefully take them out and serve immediately.

Notes

Below you’ll find my best estimate of this recipe’s nutrition facts. Treat the numbers as a guide rather than a rule—great food should nourish both body and spirit. Figures are approximate, and the website owner assumes no liability for any inaccuracies in this recipe.