Boil thick coconut milk in a saucepan until the oil is extracted and the precipitate forms into a dark brown color. This is called latik. Drain the latik from the oil and set aside. Grease a 13-inch rectangular dish with coconut oil. Set aside.
In a medium saucepan, blend rice flour, sugar, cornstarch, and fresh coconut milk. Stir in grated buko (if used). Boil over slow heat, stirring constantly to prevent lumps, until mixture is clear for about 3-5 minutes.
Pour hot mixture into prepared dish and allow to set. Sprinkle latik on top. Cool before slicing.