In a large bowl, stir together 1/2 cup water and yeast. Let stand for 5 minutes. Meanwhile, in a small saucepan, heat and stir milk, sugar, butter, and salt just until warm (120 degrees F to 130 degrees F) and butter almost melts. Stir milk mixture into yeast mixture until combined. Stir in combined mashed sweet potato, ginger, Thai seasoning (if desired), and pumpkin pie spice. Stir in flour (dough will be sticky). Lightly coat a medium bowl with cooking spray; transfer dough to the greased bowl. Lightly coat a sheet of plastic wrap with cooking spray; cover bowl with the greased plastic wrap and chill overnight.
Using a dough scraper or spatula, carefully loosen dough from bowl and turn out onto a floured surface. Cover with the greased plastic wrap and let stand for 30 minutes.
Grease a baking sheet; sprinkle lightly with cornmeal. Pat dough into an 8-inch square. Cut into sixteen 2-inch squares; place 2 inches apart on the prepared baking sheet. Cover and let rise in a warm place until nearly double in size (about 1 hour).
Preheat oven to 400 degrees F. Bake about 15 minutes or until golden brown. Remove from baking sheet; cool on a wire rack. If desired, serve with Cinnamon Butter.
In a small bowl, stir together butter, granulated sugar, and ground cinnamon.