Prepare the cake portion by slicing the cake into 1/4-inch thick by about 3-inch long slices. This is just approximate -- Layer the slices onto a platter, overlapping each piece just a bit. Make sure that the platter has a little lip to contain the custard and keeping it from spilling over. Completely cover the platter with the sliced cake. Cover and set aside.
Make the custard by combining in a sauce pan, 1 1/3 cups water, bring this almost to a boil. Add the evaporated milk and the sugar. Mix the remaining water with the cornstarch and vanilla. Gradually add this to the milk mixture, making sure to stir constantly so not to scorch the custard.
Once thickened, remove from heat and add the butter; whisk in the beaten eggs a little bit at a time, making sure to stir constantly and combine well. Pour the hot custard over the prepared cake and spread over to completely cover the cake slices.
Sprinkle the cinnamon over the entire custard and let set. The amount depends on how much you like cinnamon. You could place this in the refrigerator or keep at room temperature, and once cooled completely, it's ready to serve.
I hope you enjoy this dessert as much as the islanders do -- .
Variation: This dessert can also be prepared using pound cake or the recipe for Brojas cake, that I also have posted.