Instructions

1. For the pie dough: Heat oven to 400°. Whisk flour, milk powder, and salt together in a bowl. Mix in shortening with your hands until lumps the size of marbles form (do not overmix). Make a well in center and pour in 3 tbsp. water. Dig in and pull mixture up and over, without squeezing, until a soft dough forms. Pat dough into a 5" disk and transfer to a lightly floured surface.
2. Roll dough out into an 11"-wide circle and transfer to a 10" disposable aluminum pie pan. (Press together any tears.) Press dough against edges of pan to trim away edges. Place another 10" pie pan inside, sandwiching the dough; press down gently. Bake pie shell upside down on a baking sheet until golden brown, 20–25 minutes. Let cool, then invert pie and remove top pan. Set pie shell aside.
3. For the custard: Bring 4 1⁄3 cups milk to a boil in a medium pot over medium-high heat. Meanwhile, whisk together sugar, cornstarch, eggs, and salt in a large bowl. Drizzle hot milk into egg mixture while whisking constantly. Return mixture to pot and cook, stirring constantly, over medium heat until very thick, 15–17 minutes. Stir in untoasted coconut. Transfer coconut custard to a large bowl, cover surface with plastic wrap, and let cool to room temperature.
4. Transfer custard to pie shell. Put topping mix and remaining milk into a large bowl; beat to stiff peaks. (Alternatively, you may use sweetened whipped cream, but it won't hold up as long.) Transfer topping to a pastry bag fitted with a star tip and pipe onto pie in 3 rows, zig-zagging to create swirls. Sprinkle toasted coconut over top. Chill 3–4 hours before serving.