• 3/4 cup finely chopped onion
• 1 cup finely chopped leek, washed well and drained
• 2 large garlic cloves, minced
• 3 large carrots, sliced thin
• 1 bay leaf
• 3 tablespoons unsalted butter, or olive oil
• 2 pounds (about 3 large) sweet potatoes, peeled, halved lengthwise, and sliced thin
• 7 cups water or broth, plus additional for thinning the soup if desired

• 3/4 cup chopped pecans
• 2 tablespoons unsalted butter

Preparation

Make the soup:

1. Melt the butter (or heat the olive oil) over moderate heat and cook the onion, leek, garlic, and carrots with the bay leaf, stirring, until the vegetables are softened.
2. Add the sweet potatoes & the 7 cups water or broth, and simmer the mixture, covered for 15 to 20 minutes (or until the potatoes are very tender).
3. 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.
4. Add any additional broth/water to thin the soup to the desired consistency, and season the soup with salt and pepper.
5. Make the buttered pecans:  In a skillet cook the pecans in the butter with salt to taste over moderate heat, stirring occasionally, for 10 minutes, or until they are golden brown, and transfer them to paper towels to drain. (The pecans may be made 2 days in advance and kept in an airtight container or a resealable plastic bag.)
6. Divide the soup among bowls and top each serving with some of the buttered pecans.