01 - Preheat oven to 350°F. Place the unbaked pie crust into a 9-inch pie pan, crimp or trim the edges as preferred.
02 - In a medium saucepan, combine whole milk and heavy cream. Heat gently over medium until steaming but not boiling. Remove from heat.
03 - In a mixing bowl, whisk eggs, granulated sugar, cornstarch, vanilla extract, ground cinnamon, and salt until smooth.
04 - Slowly pour the warmed milk mixture into the egg mixture, whisking continuously to temper and fully integrate.
05 - Pass the custard mixture through a fine-mesh sieve into a clean bowl to achieve a silky texture.
06 - Pour the strained custard filling into the prepared pie crust.
07 - Transfer to the oven and bake for 45 to 50 minutes, until the center is set yet slightly wobbly. Shield crust edges with foil if browning too quickly.
08 - Remove from the oven and cool on a wire rack. Allow custard to finish setting as it cools to room temperature.
09 - Evenly sprinkle the top with ground cinnamon. Dust with powdered sugar if desired.
10 - Refrigerate for at least 2 hours before slicing and serving.