- 3 tablespoons unsalted butter
- 4 leeks (about 1 1/2 inches in diameter-4 cups chopped)
- 14 ounces Yukon potatoes (3 or 4 potatoes)
- 1 quart vegetable or chicken stock
- 1 cup buttermilk (if you don’t have buttermilk, curdle it with a tablespoon of vinegar or lemon juice)
- 1 cup heavy cream
- 1 teaspoon white pepper
- Kosher salt
Cut the root end and dark green leaves off of the leeks. Cut each one in half-length wise and place in a large bowl of cold water. Swish and shake them to get the dirt out. Dry thoroughly. Cut each one into 3 strips length-wise, then chop them across the entire length of the strip.
In a large soup pot, heat 3 tablespoons of unsalted butter over medium heat. Once the butter has heated up, add your leeks. Stir them a bit to coat in the butter and add a healthy pinch of salt, at least a teaspoon. Then, turn your heat down to medium-low. You don’t want to hear the leeks sizzling or see them getting brown or sautéing; you want them to sweat and stay nice and green. Cook for 25 minutes.
Add the potatoes and stock, and bring the pot to a boil. Once it boils, turn the heat down to a simmer; cover and let it cook for 45 minutes. Remove the lid, and blend the potatoes and leeks with an immersion blender. If you don’t have an immersion blender, you can blend it in batches in a food processor or a regular blender. Just be careful, it is very hot.
Once everything is blended well, add the cream to the buttermilk before you pour it into the soup. Add it to the soup and blend again (if you are using a food processor or regular blender, you can do this before you return the soup to the pot). At this point, you can ladle it into bowls and serve it hot or chilled before serving.