There are two varieties of sweet potatoes. One type has pale yellow flesh with a crumbly dry texture similar to that of a white potato. The other type has darker orange flesh that is sweet and moist. For the prettiest color and richest flavor, use an orange-fleshed sweet potato.
To make a vegetarian casserole, omit the sausage and use vegetable broth in place of the chicken broth.
For a chill-chasing menu, serve this casserole with warm biscuits and honey, plus mugs of hot orange-spice tea.