In a saucepan, whisk together the sugar, corn starch and salt. Add the egg yolks, and 1/2 cup of the coconut milk, whisking until smooth. Gradually whisk in the remainder of the coconut milk.
Over medium heat, cook the pastry cream, whisking constantly. After about 7-8 minutes, it should start to boil and thicken. Once it boils, continue to cook for 2 more minutes, still whisking constantly.
Remove the pan from the heat, and stir in the vanilla bean paste and butter, until melted and smooth. Stir in the coconut flakes.
Immediately pour the filling into the pre-baked crust. Let cool at room temperature for about an hour, then cover loosely with plastic wrap and refrigerate until cooled and set, several hours, or overnight.
Before serving, prepare the whipped cream. With an electric mixer, whip the cream and vanilla extract until soft peaks form. Add the powdered sugar and continue to whip until the cream is thick enough to hold its shape.
Pipe, spread or dollop the whipped cream on top of the pie. Sprinkle with a little more coconut flakes for garnish.
Leftover pie should be covered loosely and refrigerated, for up to 5 days.