6 to 7 large sweet potatoes (about 5 pounds), peeled and cut into 1-inch cubes
4 celery ribs, chopped
2 green onions, thinly sliced
1 cup fat-free mayonnaise
1/2 cup reduced-fat sour cream
2/3 cup chopped pecans, toasted
Place sweet potatoes in a Dutch oven and cover with water. Bring to a boil. Reduce heat; cover and cook for 10-15 minutes or just until tender. Drain. Transfer to a large bowl; cool to room temperature. Stir in celery and green onions.
In a small bowl, combine mayonnaise and sour cream. Gently stir into potato mixture. Cover and refrigerate for several hours or overnight. Just before serving, sprinkle with pecans.