01 - Preheat oven to 350°F (175°C). Fit the unbaked 9-inch pie crust into a pie pan and crimp or trim the edges as desired.
02 - In a medium saucepan, combine whole milk and heavy cream. Warm gently over medium heat until steaming but not boiling, then remove from heat.
03 - In a mixing bowl, whisk together eggs, granulated sugar, cornstarch, vanilla extract, ground cinnamon, and fine sea salt until smooth.
04 - Slowly pour the warm milk mixture into the egg mixture, whisking constantly to blend and temper the eggs.
05 - Pass the custard mixture through a fine-mesh sieve into a clean bowl for a silky consistency.
06 - Pour the custard filling into the prepared pie crust, smoothing the top if needed.
07 - Bake for 45-50 minutes until the center is just set but slightly wobbly. Tent the crust edges with foil if browning too quickly.
08 - Remove from oven and cool on a wire rack so the custard can finish setting.
09 - Once cooled, sprinkle ground cinnamon over the top. Dust with powdered sugar before serving, if desired.
10 - Refrigerate for at least 2 hours before slicing for neatly set portions.