01 - Preheat oven to 350°F. Arrange the unbaked pie crust in a 9-inch pie pan, crimping or trimming edges as desired.
02 - In a medium saucepan, combine whole milk and heavy cream. Warm gently over medium heat until steaming, but do not let it boil. Remove from heat.
03 - In a mixing bowl, whisk together eggs, granulated sugar, cornstarch, vanilla extract, ground cinnamon, and fine sea salt until fully combined and smooth.
04 - Gradually pour warm milk mixture into the egg mixture, whisking continuously to prevent curdling and ensure a uniform custard.
05 - Strain the custard mixture through a fine-mesh sieve into a clean bowl for a silky texture.
06 - Pour the strained custard filling into the prepared pie crust.
07 - Bake for 45 to 50 minutes, or until the center is set but still slightly wobbly. If the pie crust edges brown too quickly, cover them with foil.
08 - Remove the pie from the oven and place on a wire rack. Allow to cool; the custard will set further during cooling.
09 - Sprinkle ground cinnamon on top and, if desired, dust with powdered sugar just before serving. Refrigerate for at least 2 hours prior to slicing for optimal texture.