Ingredients

Equipment Needed

• •Large heavy-bottomed pot or Dutch oven
• •Immersion blender or countertop blender
• •Wooden spoon

Instructions

1. 1

   Clean the leeks thoroughly

   Trim the root ends and dark green tops from the leeks, keeping the white and pale green portions. Halve each leek lengthwise and hold under cold running water, fanning the layers to flush out any grit hiding inside. Leeks grow in sandy soil and trap dirt between their layers. Shake dry and slice into half-moons about half an inch thick.

   Save the dark green tops for stock. They have flavor to give, just not to this soup.
2. 2

   Sweat the leeks slowly

   Melt the butter in a large heavy pot over medium-low heat. Add the sliced leeks and stir to coat. Reduce heat to low, cover the pot, and let the leeks sweat for fifteen minutes, stirring once or twice. They should soften and turn translucent without taking on any color. This slow cooking draws out their natural sweetness.

   If the leeks begin to brown, your heat is too high. Lower it and add a splash of water to cool the pan.
3. 3

   Add potatoes and stock

   Add the potato pieces to the pot, stirring them into the softened leeks. Pour in the stock. It should cover the vegetables by about an inch. Add the salt. Bring to a gentle simmer over medium heat, then reduce to low. You want lazy bubbles, not a rolling boil.

4. 4

   Simmer until tender

   Cook uncovered for twenty-five to thirty minutes, until the potatoes are completely tender and beginning to fall apart at the edges. A fork should meet no resistance. The soup will thicken as the potato starch releases into the broth.

5. 5

   Blend to your preference

   For a silky texture, blend the soup with an immersion blender directly in the pot until smooth. For a more rustic version, mash roughly with a potato masher, leaving some pieces intact. I prefer something in between: mostly smooth with the occasional bite of potato or leek.

   If using a countertop blender, work in batches and leave the lid slightly ajar to let steam escape. Hot soup in a sealed blender will spray.
6. 6

   Finish with thyme and season

   Return the soup to low heat if needed. Stir in the fresh thyme leaves and a few grinds of white pepper. Taste and adjust salt. The soup should taste deeply of leeks first, with the thyme as a quiet background note. Ladle into warm bowls and finish each serving with a drizzle of good olive oil or a small spoonful of crème fraîche.

Chef Tips

• •Homemade stock transforms this soup. If you must use store-bought, choose low-sodium and taste before adding salt. Commercial stocks can overpower the delicate leek flavor.
• •Yukon Gold potatoes give the best texture here, creamy and smooth when blended. Russets work but can turn gluey if overprocessed. Waxy potatoes like red or fingerling will not thicken the soup properly.
• •This soup is best the day it is made, when the thyme is still bright. It keeps well for three days refrigerated, but add fresh thyme when you reheat.
• •For a lighter version, use all vegetable stock and finish with olive oil instead of butter or cream. The leeks carry enough richness on their own.

Advance Preparation

• •The soup can be made up to three days ahead and refrigerated. It thickens as it sits, so thin with a little stock when reheating.
• •Add fresh thyme just before serving for the brightest flavor. Reheated thyme loses its vitality.
• •This soup freezes well for up to two months. Thaw overnight in the refrigerator and reheat gently, adding stock as needed.

Frequently Asked Questions

Nutrition Information

1 serving (about 400g)