Caramelising leeks in butter for this Slow Cooker Leek and Potato Soup, before adding the potatoes, milk and stock, will make it the most delicious Potato and Leek soup you'll eat this season. And most importantly, it will keep you coming back for more!
Leek and Potato Soup can be a very hit or miss experience for me; so this recipe was born following regular disappointment when eating out. Honestly, my thought was, “it must be able to taste better than this”. And let me tell you, it can!
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Caramelising the leeks, either on the hob or in the slow cooker, before layering the other flavours of the soup are what give it the edge over other traditional Leek and Potato soups.
A touch of double cream adds a subtle richness alongside the thick texture achieved by the blended potatoes. You need to be careful with how much you blend through (more detail below).
How to caramelise leeks in slow cooker
Hassle-free method for caramelising the leeks for this Leek and Potato Soup can be done in the slow cooker! This would work for onions too. Music to my ears!
Caramelising the leeks, much like you would caramelise onions for French Onion soup, adds a sweet, delicious, nutty depth of flavour to the soup.
If you want a hands-off method for caramelising your leeks for this recipe, then you can do it in the slow cooker too! Simply add all the ingredients into the slow cooker, cook it on High or Low (see times in recipe card below) and stir occasionally.
If you don’t have time to caramelise the leeks, you can add all the ingredients into the slow cooker and cook on High for 4 hours or Low for 8 hours, then blend until smooth. However, you won’t get the same depth of flavour compared to including the caramelisation step.
Suitable For The Whole Family
- suitable from around 6 months old
The only element I would modify is the salt content: reduce or remove the amount of salt by using reduced salt stock cubes, unsalted butter and season any adult portions after the soup has been blitzed up or after you’ve served.
I serve the soup with cubes of bread that have been soaked in it so that they can lift up pieces of bread coated in the soup with their own hands.
Ingredients for Slow Cooker Leek and Potato Soup
- Butter: I use salted butter as this adds additional seasoning but use unsalted if you prefer or you’re trying to keep salt content low (you can always add more salt at the end)
- Onion
- Leeks
- Sugar: any sugar will be suitable (caster, granulated, golden etc.)
- Garlic: I always opt for fresh garlic but you can use 1 teaspoon of garlic paste if easier
- Potatoes: I use Maris Piper variety usually, but any type of potato will be suitable
- Chicken Broth: chicken bone broth from Borough Broth Company (use code LAUREN15 for 15% off) is what I usually use, or chicken stock. You can swap for Vegetable Stock if you want to make the recipe vegetarian.
- Milk: I like using whole milk as it adds a richness in flavour, but swap for a lower fat option to reduce calories
- Double Cream
- Salt
How To Make Slow Cooker Leek and Potato Soup
Place butter, leeks and onion in your slow cooker.
Then add garlic & sugar to slow cooker. Cook on High for 4-6 hours or Low for 8-10 hours (ideally stir a handful of times throughout).
Add chopped potatoes, chicken bone broth and milk - cook on High for 4 hours or Low for 8 hours.
Pour in double cream then blitz up in food processor/blender or use a hand blender until it's totally smooth. Be careful not to over-blend as it can make the soup gloopy! See below for what causes this.
Finally, season with salt to taste and serve.
Why you shouldn't over-blend this soup
Over-blending potato soup quickly turns this gorgeous, creamy soup into a gloopy gluey mess! And thats because over-blending potato bursts the starch molecules. Two things happen:
- Starch Release: blenders, especially powerful ones like Ninja, Vitamix or immersion blenders, rapidly break apart potato cells, releasing excessive amounts of starch.
- Gluey Texture: this excess starch gels into a sticky, glue-like substance when heated, making the soup thick and gloppy rather than smooth and velvety.
So be very careful with blending! However, if you're reading this after the fact (and it's already happened) then add more liquid (milk, stock etc.) to loosen it off a little.
FAQs
You absolutely can! Just add everything (except the cream) into the slow cooker and cook on High for 4 hours or Low for 8 hours and then blend up as per method.
Yes - use plant based butter, milk and cream.
You have over-blended the soup (blended potatoes burst their starch molecules) - add more stock to loosen it off.
Storage and Reheating
Storing Leek and Potato Soup:
- fridge - approx. 4-5 days as long as your fridge is below 4C
- freezer - up to 3 months. The exact duration will be dictated by what temperature your freezer is and also where in the freezer you store it.
What type of container can you freeze soup in? When freezing soup, you can use any freezer safe container - made of plastic, glass or freezer-safe bags (as this is also a good space saver).
Reheating:
- reheat either on the hob or in the microwave until piping hot throughout
Other soup recipes you might enjoy
If you love this one, then why not try some of my other soup recipes like:
- Carrot and Coriander with Thai influences
- Chicken Noodle Soup
- Butternut Squash, Coconut and Chilli Soup
If you have any questions please leave a comment and I'll get back to you. Or I would really appreciate it if you left me a review below.
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Leek And Potato Soup (Slow Cooker recipe)
Ingredients
- 120 g salted butter
- 1 onion large
- 500 g leeks dark green parts removed then chopped
- 1 teaspoon sugar
- 3 cloves garlic
- 800 g potatoes peeled & chopped
- 750 ml chicken bone broth or chicken stock
- 750 ml whole milk
- 150 ml double cream heavy cream
- 1 ½ teaspoon salt
Instructions
- Slow Cooker Method for Caramelising Leeks - place 120 g salted butter, 500 g leeks, 1 onion, 3 cloves garlic & 1 teaspoon sugar in your slow cooker - cook on High for 4-6 hours or Low for 8-10 hours - ideally stir a handful of times throughout (minimum 4 hours required)
- Hob Method for Caramelising Leeks - add butter, leeks, onion, garlic and sugar to large pot and cook on medium heat (with the lid on) for approx 20-25 minutes (until leeks are soft). Then remove the lid, increase the heat and stir continuously for 5 minutes whilst the leeks caramelise (30 minutes required)
- Add 800 g potatoes, 750 ml chicken bone broth(or chicken stock) and 750 ml whole milk - cook on High for 4 hours or Low for 8 hours.
- Pour in 150 ml double cream then blitz up in food processor/blender or use a hand blender until its totally smooth (See Notes)
- Finally, season with 1 ½ teaspoon salt (use less or more to taste but this is what suited me) and serve
Notes
- Starch Release: blenders, especially powerful ones like Ninja, Vitamix or immersion blenders, rapidly break apart potato cells, releasing excessive amounts of starch.
- Gluey Texture: this excess starch gels into a sticky, glue-like substance when heated, making the soup thick and gloppy rather than smooth and velvety.
Janice Conner says
This soup is fabulous. I was also not a fan of leek and potato until I tried this in the slow cooker. And so easy to make and freeze. Perfect for dinner parties
Lauren says
thanks so much Janice - so happy you loved it!
Janice Conner says
Fabulous recipe and so easy. Great for a dinner party
Eileen Martial says
Fab recipe for soup season! Gonna give it a go this weekend xxx
H says
This is the best soup I have ever eaten never mind cooked! Definitely a must try 🥰