01 - Preheat oven to 350°F. Place unbaked pie crust in a 9-inch pie pan; crimp or trim edges as desired.
02 - In a medium saucepan, combine whole milk and heavy cream. Warm gently over medium heat until steaming but not boiling. Remove from heat.
03 - In a mixing bowl, whisk together eggs, granulated sugar, cornstarch, vanilla extract, ground cinnamon, and salt until smooth.
04 - Slowly pour the warm milk mixture into the egg mixture, whisking constantly until fully combined.
05 - Pour custard mixture through a fine-mesh sieve into a clean bowl to ensure an extra smooth filling.
06 - Pour the strained custard filling into the prepared pie crust.
07 - Bake on the center rack for 45 to 50 minutes, or until the center is set but still slightly wobbly. If edges brown too quickly, tent with foil.
08 - Remove pie from oven and cool on a wire rack; the custard will set further as it cools.
09 - Sprinkle with ground cinnamon and dust with powdered sugar, if desired.
10 - Chill pie in the refrigerator for at least 2 hours before slicing and serving.