01 - Preheat oven to 350°F (175°C). Gently place the unbaked 9-inch pie crust into a pie pan, crimping or trimming the edges as desired.
02 - In a medium saucepan, combine whole milk and heavy cream. Warm over medium heat until steaming, being careful not to let it boil. Remove from heat.
03 - In a mixing bowl, thoroughly whisk eggs, granulated sugar, cornstarch, vanilla extract, ground cinnamon, and fine sea salt until the mixture is smooth.
04 - Slowly pour the warm milk and cream into the egg mixture, whisking constantly to temper and create a unified custard base.
05 - Pass the custard mixture through a fine-mesh sieve into a clean bowl to achieve a silky texture. Pour the strained custard into the prepared pie crust.
06 - Transfer the filled pie to the oven. Bake for 45 to 50 minutes, or until the center is set but still slightly wobbly. If the crust edges brown too quickly, shield with foil.
07 - Remove the pie from the oven and place on a wire rack. Allow to cool at room temperature; custard will continue to set as it cools.
08 - Sprinkle surface with ground cinnamon. Optionally, dust with powdered sugar just before serving.
09 - Refrigerate the pie for at least 2 hours to ensure thorough chilling and optimal slicing.