01 - Preheat oven to 350°F. Place unbaked pie crust in a 9-inch pie pan, crimping or trimming the edges as preferred.
02 - In a medium saucepan, combine whole milk and heavy cream. Warm over medium heat until steaming but not boiling, then remove from heat.
03 - Whisk together eggs, granulated sugar, cornstarch, vanilla extract, ground cinnamon, and fine sea salt in a mixing bowl until the mixture is smooth.
04 - Gradually pour the warm milk mixture into the egg mixture, whisking constantly to temper and evenly combine.
05 - Pour the custard through a fine-mesh sieve into a clean bowl to remove any lumps and achieve a silky texture.
06 - Pour the strained custard filling into the prepared pie crust.
07 - Bake in preheated oven for 45 to 50 minutes, or until the center is set but retains a slight wobble. Shield crust edges with foil if browning too quickly.
08 - Remove from oven and cool the pie on a wire rack. The custard will continue to set as it cools.
09 - Dust the surface with ground cinnamon and, if desired, lightly sprinkle with powdered sugar. Refrigerate for at least 2 hours before slicing and serving.