Sweet Potato Soup with Buttered Pecans

In a kettle cook the onion, the leek, the garlic, and the carrots with the bay leaf and salt and pepper to taste in the butter over moderate heat, stirring, until the vegetables are softened. Add the sweet potatoes, peeled, halved lengthwise, and sliced thin, the russet potato, peeled, halved lengthwise, and sliced thin, the 5 cups broth, the wine, and the water, simmer the mixture, covered for 15 to 20 minutes, or until the potatoes are very tender, and discard the bay leaf. In a blender puree the mixture in batches until it is very smooth, transferring it as it is pureed to a large saucepan, add the additional broth to thin the soup to the desired consistency, and season the soup with salt and pepper. The soup may be made 1 day in advance, kept covered and chilled, and reheated.