Boil the sweet potato until tender, about 20 to 30 minutes. Cool, peel, mash, and set aside. (Should yield about 1 cup).
Preheat oven to 350 degrees F. Line 2 (9-inch) pie plates with thin slices of pound cake. Firmly press into bottom of pans. Set aside.
In a large bowl, beat cream cheese until fluffy. Gradually add sugar. Mix well. Add eggs, 1 at a time, beating well after each. Pour in cream. Mix well. Add mashed sweet potato. Mix well. Stir in lemon extract, vanilla extract, and nutmeg. Mix well. Pour into lined pans.
Bake 45 minutes to 1 hour, or until center is almost set. Remove from the oven and cool at least 1 hour. Remove from pan, if desired, and refrigerate until ready to serve. Garnish as desired.