01 - Set the oven to 350°F. Place the unbaked pie crust in 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, careful not to boil. Remove from heat.
03 - Whisk eggs, granulated sugar, cornstarch, vanilla extract, ground cinnamon, and sea salt in a mixing bowl until smooth.
04 - Gradually pour the warm milk mixture into the egg mixture, whisking constantly to combine evenly.
05 - Pour the custard through a fine-mesh sieve into a clean bowl to ensure a silky texture.
06 - Pour the strained custard into the prepared pie crust.
07 - Bake for 45 to 50 minutes, or until the center is set yet slightly wobbly. If crust edges brown too rapidly, shield with foil.
08 - Transfer pie to a wire rack and allow it to cool. The custard will continue to firm as it cools.
09 - Dust the top with ground cinnamon and, if desired, sprinkle with powdered sugar prior to serving.
10 - Chill in the refrigerator for at least 2 hours before slicing for clean portions.