01 - Preheat oven to 350°F (175°C). Arrange the unbaked 9-inch pie crust in a pie pan, trimming or crimping the edges as desired.
02 - In a medium saucepan, combine whole milk and heavy cream. Warm over medium heat until steaming, making sure not to let it boil. Remove from heat.
03 - In a mixing bowl, vigorously whisk together eggs, granulated sugar, cornstarch, vanilla extract, ground cinnamon, and salt until smooth and homogeneous.
04 - Gradually stream the warm milk mixture into the egg mixture, whisking constantly to temper and thoroughly combine.
05 - Pass the custard mixture through a fine-mesh sieve into a clean bowl to ensure a smooth filling. Pour the custard into the prepared crust.
06 - Bake for 45–50 minutes, or until the center is set but retains a slight wobble. If the crust begins to brown excessively, tent the edges with foil.
07 - Transfer to a wire rack to cool completely. Custard will continue to firm up as it cools.
08 - Sprinkle with ground cinnamon and, if desired, dust with powdered sugar. Refrigerate for at least 2 hours prior to slicing.