For the conchee: Combine cornmeal, potato, pumpkin, spices, sugar, and butter and mix well. Add raisins and grated coconut. Add just enough coconut milk to make a soft dough. Place mixture in the middle of a large sheet of foil. Fold over foil and, using fingers, compress mixture into a long sausage shape. Fold and seal open ends of foil with a double bend to ensure a tight seal. Place foil packet on a steaming basket in a large pot with 2 inches of water (curve foil packet if necessary to fit). Bring water to boil, cover pot, and steam 20 minutes.