01 - Preheat oven to 350°F. Arrange unbaked pie crust in a 9-inch pie pan, forming edges as desired.
02 - In a medium saucepan, combine whole milk and heavy cream. Warm over medium heat, stirring occasionally, until steaming but not boiling. Remove from heat.
03 - In a mixing bowl, whisk together eggs, granulated sugar, cornstarch, vanilla extract, ground cinnamon, and fine sea salt until homogenous.
04 - Gradually pour the warm milk mixture into the egg mixture, whisking continuously to prevent curdling.
05 - Pass custard base through a fine-mesh sieve into a clean bowl to ensure smoothness.
06 - Pour strained custard filling into the prepared pie crust.
07 - Bake in preheated oven for 45 to 50 minutes, or until the center is just set but slightly wobbles. Shield crust with foil if browning too quickly.
08 - Remove from oven and cool on a wire rack. Custard will firm further as it cools.
09 - Sprinkle with ground cinnamon and, if preferred, dust with powdered sugar prior to serving.
10 - Refrigerate for a minimum of 2 hours before slicing and serving.