Make the pone: Position a rack in the center of the oven and preheat to 350 ̊F. Butter a 9-inch round cake pan, line the bottom with parchment, and set aside. In a small pot, whisk together the coconut cream, dried coconut, ginger, vanilla, cinnamon, allspice, nutmeg, and salt and bring to a simmer. Remove from the heat and set aside.
In a medium bowl, stir together the brown sugar, raisins, cornmeal, and flour and set aside.
In a blender or food processor, pulse (do not run continuously) half of the sweet potatoes with half of the coconut cream mixture until nearly smooth but still grainy. Scrape into a large bowl. Repeat with the remaining sweet potatoes and the rest of the coconut mixture.
Using a silicone spatula, stir the sugar mixture into the sweet potato mixture until combined. Stir in the molasses and butter. Scrape into the prepared cake pan and bake until deep golden brown and a toothpick inserted in the center comes out clean, about 1 hour 30 minutes. Remove the cake from the oven and turn the heat to 400˚F.
Meanwhile, make the custard: In a bowl, whisk the coconut milk, brown sugar, butter, allspice, cinnamon, ginger, nutmeg, vanilla, and salt until the sugar is dissolved. Pour over the hot cake, then bake until the custard has hardened slightly, about 15 minutes. Cool completely.
To serve, run a knife around the edge of the cake, then invert onto a plate.