Ingredients
1 Tbsp peanut oil
2 Tbsp unsalted butter
1 large leek, damaged outer leaves discarded, split, washed, and finally minced (three cups)
1 lb Yukon gold potatoes, peeled and held in cold water
4 cups chicken stock
1 cup water
½ tsp salt, or more to taste
½ tsp freshly ground black pepper
1 Tbsp chopped fresh parsley or chervil
½ cup grated Gruyère cheese cheese or a dollop of softened unsalted butter (optional)
Directions
Heat the oil and butter in a large saucepan. Add the leeks and cook over medium heat for about three minutes, stirring occasionally.
Meanwhile, cut the potatoes into sticks about ¾ inch thick and slice the sticks crosswise into ⅛-inch slivers (you will have about 3½ cups). The potatoes should be kept in water after peeling, but they should not be washed after they are cut into slivers; this would wash away their starch, which helps make the soup smooth.
Add the stock, water, salt, and pepper to the leeks, then mix in the potato slivers. Bring to a boil, reduce the heat, and boil gently for about 12 minutes.
Serve the soup with a sprinkling of the parsley or chervil on top and, if you like, the grated cheese or a dollop of butter.
Notes: Use olive oil and finely slice leeks.