01 - Preheat oven to 350°F. Arrange the unbaked pie crust in a 9-inch pie pan, trimming or crimping edges as desired.
02 - Combine whole milk and heavy cream in a medium saucepan. Warm over medium heat until steaming without boiling. Remove from the heat.
03 - In a mixing bowl, vigorously whisk eggs, granulated sugar, cornstarch, vanilla extract, ground cinnamon, and sea salt until the mixture is completely smooth.
04 - Gradually pour the warm milk and cream mixture into the egg mixture, whisking constantly to gently temper the eggs and blend thoroughly.
05 - Pass the custard through a fine-mesh sieve into a clean bowl to remove any solids for a refined texture.
06 - Transfer the custard into the prepared pie crust, smoothing the surface.
07 - Bake for 45 to 50 minutes, or until the center is set but still slightly wobbly. Shield the crust edges with foil if browning too quickly.
08 - Remove the pie from the oven and place on a wire rack to cool completely. The custard will finish setting as it cools.
09 - Once cooled, lightly sprinkle with ground cinnamon and dust with powdered sugar if desired.
10 - Refrigerate the pie for at least 2 hours before slicing and serving.