01 - Preheat oven to 350°F. Place the unbaked pie crust into a 9-inch pie pan and crimp or trim the edges as preferred.
02 - Combine whole milk and heavy cream in a medium saucepan. Warm gently over medium heat until steaming, without boiling. Remove from heat.
03 - In a mixing bowl, whisk eggs, granulated sugar, cornstarch, vanilla extract, ground cinnamon, and salt until smooth.
04 - Gradually pour the warm milk mixture into the egg mixture, whisking constantly to temper and blend.
05 - Strain the custard through a fine-mesh sieve into a clean bowl for an ultra-smooth texture.
06 - Pour the prepared custard filling into the pie crust.
07 - Bake for 45 to 50 minutes, or until the center is set but retains a slight wobble. Tent crust edges with foil if browning too quickly.
08 - Remove the pie and allow to cool completely on a wire rack; the custard will continue setting as it cools.
09 - Sprinkle the cooled pie with ground cinnamon and dust with powdered sugar before serving, if desired.
10 - Refrigerate for at least 2 hours before slicing for clean portions.