INGREDIENTS
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Serves 4
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1 tablespoon peanut or vegetable oil
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2 tablespoons unsalted butter
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1 large leek, damaged outer leaves discarded, split, washed, and finely minced (3 cups)
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1 pound Yukon Gold potatoes, peeled and held in cold water
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4 cups (1 quart) homemade chicken stock or canned low-sodium chicken broth
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1 cup water
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1/2 teaspoon salt, or more to taste
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1/2 teaspoon freshly ground black pepper
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1 tablespoon chopped fresh parsley or chervil
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1/2 cup grated Gruyère cheese or a dollop of softened unsalted butter (optional)