By Brigit Binns
Sauté the vegetables
In a large saucepan over medium heat, melt the butter. Add the celery and leek and sauté until the leek is translucent, about 3 minutes. Add the sweet potatoes and broth, raise the heat to high, and bring to a boil. Reduce the heat to low, cover, and simmer until the sweet potatoes are tender, about 30 minutes.