Place sweet potatoes in a medium saucepan with water to cover. Bring to a boil. Cover and cook 20 minutes or until tender; drain. Let cool to the touch; peel and mash.
Combine mashed sweet potatoes, milk, sugar, and salt; beat well. Stir in Masa Harina, mixing until well blended. Turn dough out onto a lightly floured surface; knead 5 minutes. Divide dough in half, and cover with plastic wrap.