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There’s nothing quite like a bowl of homemade soup. Yes, it takes more effort than opening a tin, and it’s far cheaper than the posh soups in the supermarkets these days, and a good deal better too.
I had leeks and potatoes to hand the other day and thought, why not make a leek and potato soup? It’s a classic comfort soup, and one I love making. Then I had one of those rare moments of inspiration. I was planning to top it with sourdough croutons when I thought: why should French onion soup have all the fun? I had some Gruyère in the fridge and a loaf of wholemeal sourdough I love, so I finished the soup with a slice of toast piled high with grated cheese. Two to three minutes under the grill and a lovely but humble bowl of soup becomes something very special.
I don’t see why that bubbling cheese topping should be reserved for French onion soup. So there you have it: a bulletproof leek and potato soup recipe. If you’d rather leave off the topping, that’s perfectly fine, as the soup is delicious on its own. To keep it healthier, I think the soup tastes creamy without adding any cream; cream is a decadent addition. Enjoy!
1 Why this leek and potato soup works
Leeks and potatoes are about as humble as ingredients get, so the method matters more than the shopping list. Three things make the difference here.
Slowly sweated leeks. The leeks and onion are cooked gently in butter under a lid for 10–12 minutes, until very soft and sweet. Don’t let them brown; this slow sweat is where the flavour comes from, and browning turns the soup muddy in colour and taste.
Bone broth. Richer and more gelatinous than ordinary stock, it gives the soup a silkier body. It can be saltier too, so taste as you season.
Creamy without the cream. The potatoes and leeks make the soup naturally creamy already, so the cream is optional. If you want a more decadent bowl, 75ml of double cream rounds it off without masking the leeks.
Leeks are a British autumn and winter staple, in season from early autumn through to spring, which makes this one of the best soups to cook as the evenings draw in.
2 Tips for making the best leek and potato soup
I tested this recipe several times before settling on the version here. These are the changes that made the biggest difference.
Weigh the leeks, don’t count them. Four medium leeks sounds like plenty, but sliced and with the green included, mine came in at only 430g, which made a thin soup. You want around 550g of leek and onion together. A chopped onion makes up the difference easily, and plenty of classic versions include one anyway. If your leeks are larger and already reach 550g, leave the onion out.
Use the green parts. Trim the roots and only the toughest, darkest tops. Most of the green is perfectly good, and you need the weight. Slice the leeks and swish them in a large bowl of cold water, then lift them out with your hands so the grit stays behind in the bowl.
Season when the broth goes in. Seasoning at the end alone leaves the soup flat. Season well as the broth goes into the pan, then taste and season again after blending. Leeks and potatoes are both mild, so this soup needs more salt and pepper than you might expect.
Add the thyme with the potatoes. A tablespoon of thyme leaves gives the soup a savoury, slightly woody note that stops it tasting one-dimensional.
Blend until just smooth. Overworked potato turns gluey, so stop as soon as the soup is silky. If using a jug blender, fill it no more than half full and hold the lid down with a folded tea towel.
Toast the bread on both sides first. This is what stops the Gruyère toast from collapsing into the soup. Grate the cheese rather than slicing it, as it melts evenly and browns better under the grill.
Nutmeg and chives go over the toast, not in the pan. I originally planned to stir the nutmeg in after blending. Grating it over the finished bowl works better, because you get the aroma as it reaches the table. The chives go on at the same moment and bring freshness and colour to a bowl that is otherwise pale and rich.
Careful when grilling over the bowls. I put the bowls under the grill to melt the cheese, as I think it lets you sprinkle more cheese onto the soup. The bowls get hot, though, so be careful when removing them from the grill. If the grill is hot, they only need a couple of minutes. Also make sure your bowls are heatproof. Grilling the toasts separately on a tray and floating them on top gives a similar result without the risk.
3 Other ways to top leek and potato soup
The Gruyère toast is my favourite, but it isn’t the only way to finish a bowl.
Wholemeal croutons. Fry 2cm cubes of thick wholemeal bread in olive oil until golden and crisp, then add them at the table so they stay crisp. A slice of bread should make enough croutons for two bowls of soup.
A swirl of cream or crème fraîche. The simplest finish. Swirl a little over each bowl as you serve, then add the nutmeg, chives and a grinding of black pepper. It keeps the soup as a light first course rather than a supper.
A herb oil. A drizzle of basil or chive oil adds a bright, grassy contrast to the sweetness of the leeks.
4 Leek and potato soup in a soup maker or slow cooker
You can make this soup without a hob. Both methods need the same two things: cook the leeks gently first for flavour, and blend the soup at the end if your machine doesn’t do it for you. Ive not got either so you might want to check timings.
Soup maker
Cook the leeks and onion in the butter first, using your machine’s sauté setting if it has one or a pan if not, until very soft and sweet. Add the potatoes, thyme, salt and pepper and enough broth to stay below the maximum fill line, which means you may not fit the full litre in. Run the smooth soup programme. If your machine only heats and doesn’t blend, blend the soup with a stick blender afterwards. Loosen with a little more hot broth if needed, stir in the cream if using, then taste and season again.
Slow cooker
Sweat the leeks and onion in the butter in a pan for 10–12 minutes, then tip them into the slow cooker with the potatoes, thyme, broth, salt and pepper. Cook on low for 6–7 hours or on high for 3–4 hours, until the potatoes are very soft. A slow cooker doesn’t blend, so blend the soup in the pot with a stick blender, or in batches in a jug blender, until just smooth. Stir in the cream if using, warm through and season again.
5 What to serve with leek and potato soup
With the Gruyère toast on top, this soup is a supper in its own right, and a crisp green salad with a sharp mustard dressing is all it needs alongside. Served without the toast, it makes a lovely starter, though keep the portions small as it is filling. Or serve it as lunch with a hunk of crusty bread and good salted butter.
6 How to store, freeze and reheat leek and potato soup
Fridge. Cool the soup quickly, then keep it in a covered container in the fridge for up to three days.
Freezer. The soup freezes well for up to three months. If you’re using cream, freeze the soup before adding it, then stir the cream in when reheating.
Reheating. Warm it gently in a pan over a low heat, stirring often, and loosen with a splash of hot water or broth if it has thickened. Don’t let it boil once the cream is in.
Toasts and croutons. Make the Gruyère toasts fresh for each serving. Croutons keep in an airtight container for up to three days, and can be refreshed in a hot oven for a few minutes if they soften.
7 Leek and potato soup variations
Vichyssoise. Serve it cold. Chill the soup thoroughly, stir in the cream once it is cold, and finish with chopped chives. Season it generously, as chilling dulls flavour.
Vegetarian. Swap the bone broth for a good vegetable stock. The soup will be lighter, so you may want a little extra seasoning.
Different cheese. Comté, Emmental or a mature Cheddar all melt and brown well under the grill if you don’t have Gruyère.
8 Leek and potato soup FAQs
Can you freeze leek and potato soup?
Yes, for up to three months. If you’re using cream, freeze the soup before adding it and stir the cream in when you reheat.
What potatoes are best for leek and potato soup?
Floury or all-rounder potatoes, such as Maris Piper or King Edward, break down easily and give a smooth, creamy soup. Peel them, as skins leave the soup speckled and a little dull.
Do you use the green part of the leek?
Yes. Trim only the roots and the toughest, darkest tops. The pale green adds flavour, colour and the weight you need for a full-bodied soup.
How do you wash leeks properly?
Halve them lengthways, slice, then swish the pieces in a large bowl of cold water. Lift them out by hand so the grit stays at the bottom of the bowl.
Why is my leek and potato soup bland?
Usually it is under-seasoned. Season when the broth goes in, then taste and season again after blending. Cooking the leeks slowly without browning also builds the flavour.
Why did my soup turn gluey?
Potatoes release starch when overworked. Blend only until the soup is smooth, and avoid blending for longer than you need to.
How do you thicken or thin leek and potato soup?
If it’s too thick, stir in a splash of hot water or broth. If it’s too thin, simmer it a little longer before blending, or check that you used enough leek and onion, around 550g in total.
Can I make leek and potato soup without cream?
Yes. The potatoes and leeks make it naturally creamy, so the cream is optional. Leave it out for a lighter soup, or stir in a splash at the end for a richer, more decadent finish.
Can I make leek and potato soup in a slow cooker?
Yes. Sweat the leeks and onion in a pan first, then cook everything with the broth on low for 6–7 hours or on high for 3–4 hours. Blend the soup in the pot at the end, as a slow cooker won’t do it for you.
Can I make leek and potato soup in a soup maker?
Yes. Sweat the leeks first, then add everything to the jug and run the smooth soup programme, keeping the liquid below the maximum fill line. If your machine doesn’t blend, finish the soup with a stick blender.
Can I use stock instead of bone broth?
Yes, any good chicken or vegetable stock works. Bone broth gives a richer body, but shop-bought stock can be saltier, so season carefully.
Can I make leek and potato soup ahead?
Yes. It keeps in the fridge for up to three days and often tastes better the next day. If you’re using cream, add it when reheating, and make the Gruyère toasts fresh.
Traditionally hot, but the cold version is called vichyssoise. See the variations above.
9 Recipe; Ingredients & Method
Leek and Potato Soup with a Melting Gruyère Toast
Print RecipeInstructions
Method
Prepare the leeks. Trim the roots and only the toughest, darkest tops: most of the green is perfectly good and you need the weight. Halve the leeks lengthways and slice into 1cm (½ inch) half-moons. Tip into a large bowl of cold water, swish them around to loosen any grit, then lift them out with your hands, leaving the grit behind in the bowl.
Weigh the leeks. You’re aiming for about 550g (1¼ lb) of leek, or of leek and onion together. Four medium leeks came in at 430g when I made this, so I made up the difference with a chopped onion. For an all-leek soup, use around five medium leeks and leave the onion out. If your leeks are larger and already reach 550g, leave the onion out.
Sweat the leeks. Melt the butter in a large, heavy-based pan over a low heat. Add the leeks, the onion if using, and a good pinch of salt, stir to coat, then cover with a lid and cook gently for 10–12 minutes, stirring occasionally, until very soft and sweet. Don’t let them brown.
Add the potatoes and thyme. Stir in the diced potatoes and the thyme and cook for a minute, turning everything through the buttery leeks.
Add the broth and season. Pour in the bone broth and season well with salt and black pepper at this point, rather than waiting until the end. Bring to the boil, then turn down and simmer, partly covered, for 15–20 minutes until the potatoes break up easily when pressed against the side of the pan.
Blend. Blend the soup until smooth with a stick blender, or in batches in a jug blender, filling it no more than half full and holding the lid down with a folded tea towel. Blend only until smooth: overworked potato turns gluey.
Finish and check the seasoning. Return the soup to a low heat and, if using, stir in the cream and warm through without boiling. Now taste properly and season again: leeks and potatoes are mild, and this soup needs more salt and pepper than you might expect to come alive. If it’s too thick, loosen with a splash of hot water or broth.
Make the Gruyère toasts. Heat the grill to high. Toast the bread on both sides, either in a toaster or under the grill, until dry and golden. Lay the toasts on a baking tray, pile the grated Gruyère on top, right to the edges, and grind over some black pepper. Slide under the hot grill for 2–3 minutes until the cheese is melted, bubbling and just starting to brown at the edges.
Serve. Ladle the soup into warmed bowls and float a Gruyère toast on each one. Grate a little nutmeg over the top, scatter over the chopped chives and serve straight away.
