Mix 3 tbsp of cornstarch, 3 tbsp sugar, and 1/4 cup water to form a slurry.
Pour one can of coconut milk in a saucepan and heat on medium heat until mixture begins to steam but is not bubbling.
Pour cornstarch slurry into the coconut milk, continuously whisking to avoid forming clumps. Coconut milk should thicken very quickly. When it reaches a gravy like consistency, turn off the heat and pour into a heatproof mixing bowl.
Stir 4 oz of chocolate into the warm coconut milk mixture until chocolate is melted and fully mixed.
Pour chocolate coconut mixture into prepared crust. Smooth out the top with a knife if needed. Place the pie in the fridge or freezer to cool. I recommend waiting at least 30 minutes for the top of the chocolate layer to set, but I've been successful with as little as 10 minutes when working very carefully.
Repeat steps 1-3 to make another haupia batter.
Very very carefully pour the haupia on top of the chocolate layer, trying to keep the haupia sitting on top of the chocolate instead of piercing straight down to the bottom.
Place the pie into the fridge to set completely. If you are not topping with whipped cream, you can leave the pie uncovered. Otherwise, plastic wrap directly touching the top coconut layer will prevent a skin from forming as the pie cools.
Let pie set until firm, at least 3 hours but preferably overnight.