Potato leek soup

Why Yukon Golds

Yukon Gold potatoes are medium-starch. They blend into a smooth, buttery soup. Russets work, but they are high in starch and turn gluey quickly if blended too long; they are at their best mashed rather than blended, in a chunky potato soup. Waxy red potatoes make a thinner soup with a slightly gummy texture. If you only have russets, use them and blend them a little less.

Don't overblend

Potato soup turns from creamy to gluey when it is blended too long. The blades burst the potato's cells and release their gelatinized starch into the liquid. A stick blender for 30 to 60 seconds is right. A countertop blender on high works faster and is easier to overdo, so pulse it and stop as soon as the soup is smooth. If you use a countertop blender, fill it no more than half full, vent the lid and hold a towel over it: hot soup expands and can blow the lid off. If you like some texture, blend half and stir it back into the rest.

Sweat the leeks, don't brown them

The covered pot and low heat in step two let the leeks cook in their own steam until they are soft and sweet. Browned leeks taste good, but they turn the soup beige and a little bitter. Leeks have a mild, sweet onion flavor that you only get by cooking them gently.

Leeks hold grit between their layers, which is why you slice them before washing them. Once sliced, the layers separate in the water and the dirt sinks. Lift the leeks out instead of pouring them into a strainer, or the grit goes right back on top.

Lighter or richer

Half a cup of half-and-half across six bowls is enough to make the soup taste creamy, because the potatoes do most of the work. Here is how the options compare:

• Lighter: whole milk instead of half-and-half saves about 15 kcal a bowl. Or leave out the dairy entirely: the potatoes alone make a perfectly creamy soup.
• Richer: heavy cream instead of half-and-half adds about 40 kcal a bowl.

Vegetarian and vegan potato leek soup

For a vegetarian potato leek soup, use vegetable broth. Everything else in the recipe is already vegetarian. Vegetable broth makes a soup that is a little sweeter and lighter than one made with chicken broth, with less savory depth. To make up for it, season a bit more boldly at the end with salt and pepper, or stir in 1 teaspoon of white miso with the half-and-half. Pick a light-colored broth: some store brands are heavy on carrot and tomato and turn the soup orange.

For a vegan version, also cook the leeks in 2 tablespoons of olive oil instead of butter, and finish with 1/4 cup of unsweetened oat milk instead of the half-and-half. A bowl then has about 220 kcal.

Instant Pot or crock pot

Instant Pot: sweat the leeks on Sauté, add the potatoes, broth and herbs, and cook 6 minutes at high pressure with a 10-minute natural release. Then blend and finish as above.

Crock pot: sweat the leeks in a skillet first, because they will not soften properly in the slow cooker. Then put them in the slow cooker with the potatoes, broth and herbs and cook on low for 6 to 7 hours or on high for 3 to 4, until the potatoes break easily. Blend and finish as above.

Vichyssoise: potato leek soup served cold

Chilled potato leek soup is vichyssoise, a classic summer soup. Blend it very smooth, chill it overnight, and thin it with a little cold broth or milk, because it thickens a lot in the fridge. Cold food needs more seasoning than hot, so taste it again and add more salt after chilling. Our green pea soup is the other good one to serve cold.

Keeping it

Four days in the fridge. It freezes for 3 months. The potato turns slightly grainy on thawing, but it comes back fine if you blend it again briefly after reheating. Freeze it before adding the half-and-half, and stir that in when you reheat.

What it is worth nutritionally

About 235 kcal a bowl, with 6 g of protein and 7 g of fat. That is well below a restaurant-style potato soup made with heavy cream. Potatoes are better nutritionally than their reputation suggests. A medium potato has more potassium than a banana, along with vitamin C and B6. Leeks bring a type of fiber called inulin, which feeds beneficial gut bacteria. The same fructans can bother people with IBS, since leeks are high in FODMAPs; see our guide to the low-FODMAP diet. To make the soup a full meal, serve it with a salad with chicken or eggs, or blend a can of white beans into the pot.