Leeks, which are sweeter and more subtle than onions, are said to last in the refrigerator for two weeks, but I find that they often become slimy so I purchase them only when I need them.
Most books recommend that you wash leeks under cold running water, but I’ve discovered that rinsing in hot water works better for getting the dirt out. Since most of the time you are going to cook them, it doesn’t affect their taste or texture. Trim off the roots and all but the first inch or so of green, slice the leek lengthwise, open it up and rinse several times.
2 tablespoons unsalted butter
1 bunch leeks, white part only, finely chopped
2 pounds new potatoes, peeled, if desired, and diced
2½ to 3 cups cold water
¾ teaspoon kosher salt
¼ to ½ teaspoon white pepper
1. Place a large skillet over medium heat and, when it is hot, add the butter. Add the leeks and cook until they are soft and golden, about 12 minutes Raise the heat to high, add the potatoes and 2½ cups of the water and bring to a boil. Cook until the potatoes are tender, about 20 to 25 minutes. If necessary, add the remaining ½ cup water. Mash with a fork or potato masher and gradually add the cream, salt, and pepper. Reheat over very low heat, if necessary. Serve immediately.
From The $50 Dinner Party: 26 Dinner Parties That Won’t Break Your Bank, Your Back, or Your Schedule (Simon & Schuster, 1998)