01 - Preheat oven to 350°F. Place the unbaked pie crust into a 9-inch pie pan, shaping the edges as desired.
02 - In a medium saucepan, combine whole milk and heavy cream. Warm gently over medium heat until steaming but not boiling, then remove from heat.
03 - In a mixing bowl, whisk eggs, granulated sugar, cornstarch, vanilla extract, ground cinnamon, and fine sea salt until the mixture is smooth.
04 - Gradually pour the warm milk mixture into the egg mixture while whisking continuously to blend and temper.
05 - Strain the blended custard through a fine-mesh sieve into a clean bowl to ensure 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 with a slight wobble. Shield crust edges with foil if browning too quickly.
08 - Remove from oven and cool on a wire rack. Allow custard to finish setting as it cools.
09 - Sprinkle the top with ground cinnamon and, if desired, dust with powdered sugar before serving.
10 - Refrigerate for at least 2 hours before slicing for clean servings.