01 - Preheat oven to 350°F. Fit the unbaked pie crust into a 9-inch pie pan, crimping or trimming the edges as desired.
02 - In a medium saucepan, combine whole milk and heavy cream. Warm gently over medium heat until steaming without boiling, then remove from heat.
03 - In a mixing bowl, whisk together eggs, granulated sugar, cornstarch, vanilla extract, ground cinnamon, and salt until completely smooth.
04 - Slowly add the warmed milk mixture to the egg mixture, whisking constantly to gently combine and avoid curdling.
05 - Pour custard base through a fine-mesh sieve into a clean bowl to achieve a silky texture.
06 - Pour custard filling into the prepared pie crust. Transfer to the oven and bake for 45 to 50 minutes or until center is set yet slightly wobbly. Shield crust edges with foil if browning too rapidly.
07 - Remove from oven and cool completely on a wire rack. Custard will continue to firm up as it cools.
08 - Dust top of pie with ground cinnamon and, if desired, a light sprinkle of powdered sugar. Chill in the refrigerator for at least 2 hours before slicing and serving.