Six ingredients, twenty minutes, a blender, a winter Tuesday solved. The soup that justifies still owning a blender.
Why you should cook this
The first time I made potato and leek soup I served it to my father-in-law, who had grown up on the Welsh side of his family making this exact dish in slightly different proportions. He took one mouthful, paused for what felt like an unreasonable length of time, and said “you’ve under-leeked it.” He was right. I had used one leek when I should have used three. The soup was potato soup with the suggestion of leek, when potato and leek soup should be leek soup with the body of potato. He went on to give me a lecture on the leek-to-potato ratio that I now carry with me into every kitchen I cook in. The man was wasted on accountancy.
The ratio is two leeks to one potato by weight. Not by piece, by weight. Leeks are mostly water and air; potatoes are mostly starch. Two leeks weigh roughly the same as one large floury potato. This makes the soup taste of leek, with the potato providing texture and richness, instead of the other way around. Use the white and pale-green parts of the leeks. The dark green tops are for stock, not soup. Yes, the dark greens have flavour. They also have fibrous threads that no blender will ever defeat.
Sweat the leeks slowly in butter for fifteen minutes before any liquid hits them. This is the step everyone rushes and everyone regrets. Slow sweat releases the leek sugars and turns them sweet rather than oniony. Add the diced potato, hot stock, a small bay leaf. Simmer for twenty minutes. Blend smooth. Finish with a splash of cream and check the salt. The result is a soup that costs about $4 to make, looks like something a grown-up made, and tastes like a hug from someone who reads books for fun.
What to drink with it
The soup is delicate. Match it. A Tasmanian pinot grigio or a Mornington Peninsula chardonnay with restraint. Ravensworth Pinot Gris at $25 is the everyday option. Yabby Lake Single Vineyard Chardonnay at $48 if you have invited someone who notices wine. A dry French cider also works beautifully if you have one in the fridge. For a non-alc, a properly cold elderflower cordial with sparkling water and a wedge of cucumber.
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Notes from the kitchen
Wash the leeks properly. Slice lengthwise first, then fan them out under running water and rub the layers apart. Grit lives between the layers, and grit blended into a smooth soup is the texture of disappointment. Drain on a tea towel before slicing finely. Use floury potatoes (sebago or russet, not waxy reds), they break down properly under the blender and give the soup the silken texture it wants.
Blend in a stand blender if you have one. Stick blenders work, but never quite achieve the silk of a proper jug blender. Blend in two batches, lid slightly open with a tea towel over the top to let the steam escape. A sealed lid on a hot soup will pop the top off the blender and redecorate your kitchen in cream-coloured leek soup, which is funny only in retrospect. Strain through a fine sieve if you want restaurant-smooth. Skip the sieve if you do not. The world will not end either way.
Two things that go wrong
Soup tastes oniony or bitter
Leeks were not sweated long enough, or you used the dark green tops. Sweat for a full 15 minutes in butter before any liquid hits the pan. Use only white and pale-green parts.
Texture is grainy or split
Either you over-blended (potato starch released too aggressively) or you boiled it after adding the cream (cream split). Blend until smooth, no longer. Add cream off the heat at the end and warm gently. Do not boil after the cream is in.
Variations worth knowing
Vichyssoise (the chilled version)
Same soup, served cold. Make a day ahead, refrigerate, finish with a swirl of cream and finely sliced chives. The classic French summer soup. Australians get this in February when we are pretending to be sophisticated.
With smoked bacon
Brown 100g of smoked streaky bacon at the start, set aside on paper towel. Sweat the leeks in the bacon fat. Blend the soup, scatter the bacon on top to serve. Less elegant, much heartier.
Roasted garlic version
Roast a whole head of garlic at 180°C for 40 minutes, squeeze the cloves out into the soup before blending. The flavour is rounder, sweeter, slightly nutty. Best when the leeks are not at their peak.
Leftovers and make ahead
Improves overnight. The flavours integrate, the leek sweetness becomes more pronounced, the texture stays smooth. Reheats gently on the stove with a splash of stock or water if it has thickened too much. Freezes well for three months. Do not freeze with the cream in. Add the cream after thawing and reheating. Frozen-and-reheated cream goes grainy.
The soup also makes an excellent base for a baked potato gratin. Pour into a baking dish, layer with thinly sliced waxy potato and gruyère, bake at 180°C until amber. A second meal that is technically not the same as the first.
The recipe
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Ingredients
Method
- Slice the leeks lengthwise, fan apart under running water, rub between fingers to remove grit. Drain on a tea towel, slice thinly across.
- Melt the butter and oil in a large heavy pot over low heat. Add the leeks and onion. Sweat slowly for 15 minutes, stirring occasionally. Do not brown.
- Add the diced potato, stock and bay leaf. Bring to a gentle simmer.
- Cover and simmer for 20 minutes, until the potato breaks easily under a fork.
- Remove the bay leaf. Blend the soup in two batches in a stand blender (lid slightly ajar with a tea towel over the top) until completely smooth.
- Return to the pot. Stir in the cream off the heat. Warm gently. Season with salt and white pepper to taste.
- Ladle into bowls, swirl with extra cream, scatter with chives. Serve with crusty sourdough.