Preheat your oven to 350°F (175°C) and generously grease a 9-inch round cake pan or baking dish with butter.

In a large mixing bowl, combine the grated sweet potatoes, flour, cornmeal, brown sugar, raisins, cinnamon, nutmeg, and salt until the dry ingredients are evenly distributed.

Pour in the melted butter, vanilla extract, grated ginger, rum, and 2 1/2 cups of the coconut milk, stirring thoroughly until you have a smooth, heavy batter.

Pour the batter into the prepared baking dish, smoothing the top with a spatula, and place it in the preheated oven.

Bake for roughly 60 minutes until the top begins to form a crust and the pudding is partially set.

While baking, mix the remaining 1/2 cup of coconut milk with a teaspoon of sugar to create the custard topping mixture.

Remove the pudding briefly from the oven and gently pour the sweetened coconut milk mixture over the entire surface.

Return the dish to the oven and bake for an additional 30 to 40 minutes, until the top is golden and bubbling but still slightly soft to the touch.

Remove from the oven and allow the pudding to cool completely in the pan for at least 2 hours before slicing, as the texture sets while cooling.