Begin by making the custard as it will require some time to cool. In a small saucepan, cook milk, egg yolks, sugar, and cornstarch over medium heat, whisking constantly until mixture thickens and boils. Stir in vanilla and butter. Transfer custard to a bowl, press plastic wrap onto the surface (to prevent a skin from forming on the custard) and refrigerate for about two hours.
For the crust, begin by preheating your oven to 375 degrees F. Then, mix together the graham cracker crumbs, coconut, sugar, and melted butter until combined. Press mixture evenly into an 8 or 9 inch pie plate. Bake for 7 minutes. Allow the crust to cool.
In a medium saucepan, mix one cup of blueberries with sugar, cornstarch, and water. Bring to a boil over high heat. Cook two minutes to thicken while stirring. Stir in lemon juice and butter. Remove from heat and let cool. Gently stir in remaining three cups of blueberries.
Finally, spread the chilled custard into the bottom of the chilled coconut graham cracker crust. Top with the berry mixture and refrigerate until set. About three hours.
Slice, serve, and savor!