Place ½ cup shredded unsweetened in the bowl of a food processor fitted with a steel blade. Pulse until the coconut is very finely chopped.
Combine the chopped coconut, graham cracker crumbs, ⅓ cup melted butter, 2 tablespoons sugar, and pinch of salt in a medium bowl. Stir to combine.
Spread the mixture in a 9 inch pie plate, starting with covering the sides and then the bottom of the pie plate.
Bake for 8–10 minutes, or until golden brown. Let cool.
For the first layer:
Place the mango nectar in a saucepan over medium heat. Bring to a boil and reduce, stirring occasionally, until ½ cup liquid is left.
Add the coconut milk, whole milk, and ¼ cup granulated sugar in a saucepan over medium heat. Bring to a simmer.
Meanwhile, whisk the egg yolks, cornstarch, and remaining ¼ cup sugar in a medium bowl until combined.
Once the mango mixture begins to simmer, add ½ cup of it to the egg yolk mixture, whisking vigorously. Add another ½ cup and whisk again. While continuing to whisk, pour the egg yolk mixture into the saucepan with the remaining mango mixture. Whisk vigorously while the mixture cooks and thickens, about 30–45 seconds. Remove the pan from the heat.
Whisk in the butter, vanilla, and salt.
Pour the mixture into the baked graham cracker crust. Place a piece of plastic wrap directly onto the mango mixture, pressing it over the top so that the mango mixture is covered.
Refrigerate for 4 hours, or up to 2 days.
For the second layer:
Within a few hours of serving, prepare the second layer.
In the bowl of a stand mixer, combine the cream, powdered sugar, and rum. Beat on high until soft peaks form and the mixture turns to whipped cream.
Remove the plastic wrap and spread the whipped cream over the mango layer.
Scatter the toasted large flake coconut over the top. Garnish with mango slices.