01 - Preheat oven to 350°F. Place unbaked 9-inch pie crust into pie pan. Crimp or trim edges as preferred.
02 - Combine milk and heavy cream in a medium saucepan. Warm over medium heat until steaming, without boiling. Remove from heat.
03 - In a mixing bowl, whisk eggs, granulated sugar, cornstarch, vanilla extract, ground cinnamon, and sea salt until smooth.
04 - Gradually pour warm milk mixture into the egg mixture, whisking constantly to prevent curdling.
05 - Pass the custard base through a fine-mesh sieve into a clean bowl to achieve a silk-smooth consistency.
06 - Pour custard filling into prepared pie shell. Bake 45–50 minutes until custard is set with a slight wobble in the center. Shield edges with foil if browning too rapidly.
07 - Remove pie from oven and place on a wire rack. Allow to cool to room temperature; the custard will finish setting as it cools.
08 - Sprinkle pie with ground cinnamon and, if desired, lightly dust with powdered sugar before serving. Refrigerate at least 2 hours before slicing.