01 - Set oven temperature to 350°F (175°C). Fit the unbaked pie crust into a 9-inch pie pan, trimming or crimping the edges as desired.
02 - Combine whole milk and heavy cream in a medium saucepan. Gently heat over medium, stirring occasionally, until steaming but not boiling. Remove from heat.
03 - In a mixing bowl, whisk eggs, granulated sugar, cornstarch, vanilla extract, ground cinnamon, and salt until fully integrated and smooth.
04 - Gradually pour the hot milk mixture into the egg mixture in a slow stream, whisking constantly to prevent curdling and ensure a uniform custard base.
05 - Pass the blended custard through a fine-mesh sieve into a clean bowl to remove any lumps and achieve a silky texture.
06 - Pour the strained custard filling into the prepared pie crust, smoothing the surface gently.
07 - Bake for 45 to 50 minutes, or until the custard is set with a slightly wobbly center. If the crust starts to brown quickly, protect the edges with aluminum foil.
08 - Remove from oven and set on a wire rack to cool completely. The filling will continue to set as it cools.
09 - Sprinkle ground cinnamon over the top and add a dusting of powdered sugar if desired. Transfer to the refrigerator and chill for a minimum of 2 hours before slicing.