Heat 3 cups of vegetable broth to the boiling point; reduce heat to the lowest setting to keep hot.
In a medium saucepan, melt butter; add minced shallot and pecans; cook until shallot is tender.Add rice and cook, stirring, until well blended.Stir in sweet potato. Stir about 3/4 cup of the hot broth into the rice mixture. Cook over medium-low heat, stirring constantly, until liquid is absorbed. Continue adding liquid, about 1/4 to 1/3 cup at a time, stirring frequently, until the rice and sweet potato are tender (not overly soft). The texture should be creamy a little loose. This will take about 25 minutes and about 2 to 3 cups of broth. Stir in Parmesan cheese and green onion or parsley, then taste and add salt and freshly ground black pepper to taste.
Serves 3 to 4.