01 - Preheat oven to 350°F (175°C). Arrange the unbaked 9-inch pie crust in a pie pan, then crimp or trim the edges as preferred.
02 - In a medium saucepan, combine whole milk and heavy cream. Gently heat over medium until steaming but not boiling. Remove from heat.
03 - In a mixing bowl, vigorously whisk together eggs, granulated sugar, cornstarch, vanilla extract, ground cinnamon, and salt until well combined and smooth.
04 - Gradually pour the warmed milk mixture into the egg mixture, whisking constantly to temper the eggs and fully integrate ingredients.
05 - Pour custard base through a fine-mesh sieve into a clean bowl to remove any lumps and ensure a silky texture.
06 - Transfer the strained custard filling into the prepared pie crust, spreading evenly.
07 - Bake for 45 to 50 minutes, or until the center is set but retains a slight wobble. If the crust begins to brown excessively, shield the edges with foil.
08 - Remove pie from the oven, and let cool on a wire rack. The custard will finish setting as it cools.
09 - Sprinkle the surface with ground cinnamon and, if desired, dust lightly with powdered sugar just before serving.
10 - Refrigerate for a minimum of 2 hours before slicing to ensure clean portions.