Potato Leek Soup
Potato leek soup — the French classic also known as potage parmentier — is three big leeks softened slowly in butter and olive oil, 700 g of Yukon Gold potatoes simmered in a litre of vegetable broth, and a finish of cream and chives. It is vegetarian and gluten-free as written, needs 15 minutes of prep and about 30 minutes at the stove, and most of that is a covered simmer you can leave alone. Blended just until smooth, it pours up velvety rather than gluey.
- Prep
- 15 min
- Cook
- 30 min
- Total
- 45 min
- Serves
- 4
Ingredients
What you’ll need — tap to tick off as you go
- 700 g
- 2 tbsp
- 1 tbsp
- 1 l
- 120 ml
- 1 ½ tsp
- ½ tsp
- 2 tbsp
Process
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Trim the root ends and the dark green tops off the 3 leeks, leaving the white and light green parts. Halve them lengthwise, then slice crosswise into 1/4-inch half-moons. Swish the slices in a bowl of cold water so the grit falls between them, lift the leeks out into a colander, and drain. Soil hides between leek layers, and any that reaches the pot never softens.
In a large pot or Dutch oven, melt the 2 tbsp butter with the 1 tbsp olive oil over medium heat. Add the leeks and a pinch of salt, turn the heat down, and cook for about 8 minutes, stirring occasionally, until the leeks are soft and translucent. No browning: color brings bitterness and dulls the pale soup.
Add the 700 g of potatoes and stir to coat them in the fat. Pour in the 1 litre of broth and add the 1.5 tsp salt and 0.5 tsp black pepper. Bring to a boil, then reduce the heat, cover, and simmer for about 20 minutes, until the potatoes are very tender and a knife slides through the thickest chunk with no resistance.
Take the pot off the heat. Blend the soup with an immersion blender until it is completely smooth, about 1 to 2 minutes, and stop there — extra blending whips the potato starch into a gluey paste. With a countertop blender, work in batches, fill it no more than halfway, and vent the lid: hot soup expands.
Return the soup to low heat and stir in the 120 ml cream, if using. Taste and adjust with a little more salt and pepper; if the soup is thicker than you like, loosen it with a splash of broth or water until it just coats the back of a spoon.
Ladle the soup into four warmed bowls, scatter the 2 tbsp of chives over the top, and finish with a crack of black pepper. Serve hot, while the chives are still bright and the soup is steaming.
Why this recipe works
Two things keep this soup silky rather than starchy. First, the leeks sweat slowly in fat without taking on any color: gentle heat collapses their cell walls and releases their sweet, mild onion flavor, while browning would add a darker, bitter edge and tint the pale soup. Second, potato starch. As the chunks simmer, their starch granules absorb broth, swell and soften; blending disperses that starch through the liquid, where it thickens the soup and gives it body. The same starch is why blending has a limit: keep going and the granules keep bursting, whipping the soup toward a gluey paste. Stop when it is smooth, and cream and chives finish a velvety bowl.
Equipment
- Large heavy pot or Dutch oven, 4 to 5 litres, deep enough to hold 1 litre of broth, 700 g of potatoes and 3 sliced leeks without crowding
- Immersion blender, or a countertop blender for blending in batches
- Chef's knife and cutting board for the leeks and potatoes
- Large bowl and a colander, for washing the sliced leeks free of grit
- Measuring cups and spoons, for the broth, cream and seasoning
- Wooden spoon or heatproof spatula
- Ladle, for filling four bowls
Kitchen notes
Kitchen notes
- Dry the leeks after washing — a salad spinner or a towel — before they meet the butter. Water left on the leaves steams them, dilutes the fat and slows the gentle cooking that builds the sweet base.
- Cut the potatoes into even 1-inch chunks, as the recipe calls for: bigger pieces stay hard while small ones crumble, and uneven cooking is the usual reason a blended soup turns out coarse.
- Season in two stages — the pinch with the leeks, the measured spoonfuls with the broth — and taste once more after blending. Potatoes swallow salt as they cook, so a soup that tasted right in the pot can read flat in the bowl.
- Snip the chives with kitchen scissors or a very sharp knife. A dull blade bruises the leaves, which darkens them and tastes harsher than their clean, sweet onion note.
- If you skip the cream, finish each bowl with a drizzle of olive oil: it restores some of the richness the cream would have brought, and it looks polished at the table.
Common mistakes
- Gluey texture: the soup was blended past smooth, and the wrung-out potato starch turned sticky. Blend only until it is silky — short bursts, not minutes — keep it out of a food processor, and cook with Yukon Gold, which carry less starch than floury russets.
- Gritty mouthfuls: leeks rinsed briefly under the tap still hold soil between their layers. Slice them first, swish the rings in a bowl of cold water so the grit sinks, then lift the leeks out instead of pouring the bowl through them.
- Dull, faintly bitter flavor: the leeks took on color in the pot, trading their sweet onion flavor for darker notes. Keep the heat gentle and stir while they soften; the leeks should end up soft and translucent, never golden.
- Thin, watery soup: extra broth beyond the 1 litre, or potatoes that were not fully tender and so never thickened the broth. Simmer until a knife slides through the potatoes before blending, and if the finished soup is still loose, simmer it uncovered for a few minutes to reduce, or stir in the cream.
- Grainy or scorched soup when reheated: a hard boil after the cream goes in. Reheat gently over medium-low heat, stirring now and then, and pull it off the heat once it steams; the soup should never come to a rolling boil.
Serving suggestions
- Serve in warmed bowls, straight off the stove; the soup is at its best hot, and warm bowls keep the second helping from cooling too quickly.
- Crusty bread or a warm baguette on the side — pick a gluten-free loaf to keep the meal as gluten-free as the soup itself.
- A crisp green salad with a sharp vinaigrette cuts through the cream; keep the dressing simple so it does not compete with the leeks.
- For drinks, sparkling water with a lemon wedge or iced tea keeps the palate clean between spoonfuls.
Variations
- Rustic half-mashed version: blend just half the pot and crush the rest with a potato masher, so the potato leek soup keeps some soft chunks; the flavor is the same, the texture is heartier.
- Dairy-free potato leek soup (a clearly different, dairy-free version): sweat the leeks in the same 2 tbsp olive oil instead of butter, leave out the cream or finish with the same 120 ml of unsweetened coconut milk, and keep the potato base — it still blends up creamy.
- Herb-scented version: drop 2 sprigs of thyme or 1 bay leaf into the pot with the broth, then fish them out before blending; the herbs round out the sweet leek flavor without changing the method.
Refrigerator
- RefrigeratorCool the soup within 2 hours of cooking — divide it into shallow containers so the batch chills quickly — then keep it covered in the fridge for 3 to 4 days. It thickens as it sits; stir in a splash of broth or water when you reheat.
- ReheatingWarm gently in a saucepan over medium-low heat, stirring now and then, until it is steaming hot throughout — at least 74°C if you check with a thermometer. Keep it below a boil, which can scorch the bottom and make the cream look grainy.
- FreezingFreezes well for up to 3 months: cool it, pack it with a little headspace for expansion, and thaw overnight in the fridge. Dairy can look slightly grainy after thawing, so freeze the soup without the cream if you can, and stir the 120 ml cream in when you reheat.
- Make aheadThe flavor deepens overnight, so it is a good pot to make up to 3 days ahead: cook it fully, cool it fast, refrigerate, and reheat gently. Add the chives only at the table.
Updated:
How this recipe was developed
- USDA FSIS, Leftovers and Food Safety (refrigerate cooked food within 2 hours; cool big batches in shallow containers; soups keep 3 to 4 days refrigerated; reheat leftovers to 74°C)
- USDA FSIS, Freezing and Food Safety (freezer storage chart: soups and stews hold best quality 2 to 3 months; frozen food stays safe indefinitely)
- Serious Eats, The Best Potato-Leek Soup, J. Kenji Lopez-Alt (leeks cooked slowly in butter without browning; blending bursts swollen potato-starch granules and makes soup gluey — the more you blend, the gluier it becomes; blend only until pureed)
- BBC Food, How to cook leeks and Leek and potato soup (soil traps between leek layers — slice, then wash thoroughly; sweat leeks gently without browning or the soup turns bitter; keeps 3 days refrigerated; freezes well)
Editorial references are kept internally for verification. This page makes no claim of external certification or professional testing.
FAQ
The questions we get asked most
Why did my potato leek soup turn out gluey?
Over-blending is the cause. Potato starch gives the soup its silky body, but once the swollen starch granules are worked too hard — long spins in a blender, or a food processor — the whole pot turns sticky, like paste. Prevent it by blending only until smooth, about 1 to 2 minutes and often less with an immersion blender, and by cooking with Yukon Gold, which carry less starch than floury russets. If this batch already turned gluey, a splash of hot broth loosens it slightly, but the texture only goes one way.
How do I wash leeks so they aren't gritty?
The grit hides between the layers, so wash after cutting rather than before. Trim and slice the leeks, then swish the slices in a big bowl of cold water, pulling the rings apart with your fingers; the sand sinks while the leeks float. Lift them out with your hands or a slotted spoon and drain — don't pour the bowl through them, or the grit settles right back in. Rinse the bowl and repeat if the water still looks sandy.
Can I make potato leek soup ahead of time?
Yes — it is arguably better the next day. Cook the full batch, cool it within 2 hours, and refrigerate it in a covered container up to 3 days ahead of serving; the flavor deepens overnight and the soup thickens. Reheat it gently over medium-low heat, loosening with a splash of broth, and add the chives only when you serve.
How do I know when the potatoes are done?
Go by feel, not the clock: after about 20 minutes of simmering, the tip of a knife should slide through the thickest potato chunk with no resistance at all, and the chunk should crush easily against the side of the pot. If any firmness is left, keep simmering and check every 5 minutes — undercooked potatoes blend up coarse instead of smooth.
Can I use frozen leeks instead of fresh?
Yes, and this soup is where frozen leeks shine, because it gets blended anyway. Use about 3 cups of frozen sliced leeks in place of the 3 fresh ones, add them straight to the pot, and cook until the extra moisture they release has cooked off before the potatoes go in. Expect a slightly softer texture and a slightly milder flavor; both disappear into the finished soup.
Can I freeze potato leek soup?
Yes, for up to 3 months. Freeze it without the cream if you can — dairy can separate and look grainy after thawing — and stir the 120 ml of cream in when you reheat. Cool the soup first, leave a little headspace in the containers for expansion, and thaw overnight in the fridge before reheating gently.
Why is my potato leek soup not creamy enough?
The body comes from two places: fully cooked potatoes and, if you use it, the cream. If the soup tastes thin, check the potatoes first — chunks that were not fully tender never release the starch that thickens the broth. If they were tender, the fix is simple: blend until perfectly smooth, simmer uncovered for a few minutes to concentrate the soup, or stir in the cream for a richer bowl. A little more salt also helps the soup taste fuller.
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