Have ready a cooled 9-inch deep dish crust.
In a 2-cup liquid measuring cup, combine cold water and cornstarch and whisk to make a slurry.
In a medium-sized saucepan over medium heat, whisk together the 1 cup of whole milk, can of coconut milk, and sugar and bring to a simmer. When it is simmering, whisk the cornstarch slurry again, then whisk it into the simmering mixture. Whisk until thickened. This should take about 5 to 7 minutes.
Set a clean bowl on the scale, set the tare to zero and pour about 18 oz of the mixture (around half, but a little under) into the clean bowl. You can also just eyeball it if you’d rather.
Add the chocolate to the saucepan with the remaining coconut mixture. Set over low heat and whisk just until the chocolate is fully melted.
Stir 1 teaspoon of coconut extract and ½ teaspoon vanilla into the bowl with the white coconut mixture, then stir ½ teaspoon of vanilla into the chocolate mixture. Let both mixtures cool for about 5 minutes.
Spread the chocolate mixture evenly in the pie crust. The coconut mixture will still be a little cool and runny at this point, so you may want to let it cool for another 10 minutes. Carefully spoon it over the chocolate mixture. It will not be stiff or very thick at this point.
Cover and chill for 6 hours.