2 tablespoons butter or extra-virgin olive oil 3 medium potatoes, any type, peeled and cut into small cubes 3 leeks, white and light green parts only, well washed and sliced into thin rings Salt and freshly ground red pepper 1 quart vegetable stock ½-1 cup sour cream, cream or yogurt
Put the butter or oil in a large, deep saucepan or casserole over medium heat. When the butter melts or the oil is hot, add the potatoes and leeks. Sprinkle with salt and pepper and cook, stirring, for 2 or 3 minutes. Add the stock and cook until the vegetables are very tender, about 20 minutes. Carefully purée the soup in a blender or with an immersion blender, then return it to the pot. Stir in ½ cup cream, sour cream or yogurt. Add more cream to reach desired consistency. Season with salt and pepper to taste. Chill thoroughly before serving.
Adapted from "How to Cook Everything Vegetarian" by Mark Bittman