01 - Preheat oven to 350°F (175°C). Arrange the unbaked pie crust inside a 9-inch pie pan and shape or trim the edges as desired.
02 - In a medium saucepan, combine whole milk and heavy cream. Gently warm over medium heat until steaming but not boiling. Remove from the heat.
03 - In a mixing bowl, whisk together eggs, granulated sugar, cornstarch, vanilla extract, ground cinnamon, and fine sea salt until the mixture is smooth.
04 - Slowly pour the warm milk mixture into the egg mixture, whisking constantly to temper and blend thoroughly.
05 - Pass the custard base through a fine-mesh sieve into a clean bowl to eliminate any lumps and achieve a silky texture.
06 - Pour the custard filling evenly into the prepared pie crust.
07 - Bake for 45 to 50 minutes, until the center is set with a slight wobble. Shield the crust edges with foil if browning too rapidly.
08 - Remove from the oven and allow to cool completely on a wire rack. The custard will continue to firm as it cools.
09 - Sprinkle ground cinnamon over the top and, if desired, lightly dust with powdered sugar prior to serving.
10 - Place in the refrigerator and chill for at least 2 hours before slicing.