01 - Preheat oven to 350°F. Place the unbaked pie crust in a 9-inch pie pan. Crimp or trim the edges as preferred.
02 - In a medium saucepan, gently heat the whole milk and heavy cream over medium heat until steaming, without boiling. Remove from heat.
03 - In a mixing bowl, whisk together the eggs, granulated sugar, cornstarch, vanilla extract, ground cinnamon, and salt until smooth.
04 - Slowly pour the warm milk and cream into the egg mixture, whisking constantly until fully incorporated.
05 - Strain the custard through a fine-mesh sieve into a clean bowl to ensure a silky texture.
06 - Pour the strained custard filling into the prepared pie crust.
07 - Bake in the preheated oven for 45 to 50 minutes, until the center is set but still slightly wobbly. Tent the edges with foil if browning too quickly.
08 - Transfer the baked pie to a wire rack and allow it to cool completely. The custard will continue to set during cooling.
09 - Sprinkle with the reserved ground cinnamon and dust with powdered sugar if desired.
10 - Refrigerate for at least 2 hours before slicing and serving.