01 - Preheat oven to 350°F. Place the unbaked pie crust in a 9-inch pie pan and crimp or trim the edges as preferred.
02 - Gently warm whole milk and heavy cream together in a medium saucepan over medium heat until steaming, ensuring the mixture does not boil. Remove from heat once steaming.
03 - In a mixing bowl, whisk eggs, granulated sugar, cornstarch, vanilla extract, ground cinnamon, and sea salt until completely smooth.
04 - Slowly pour the warm milk and cream mixture into the egg mixture, whisking constantly to temper and fully combine.
05 - Pass the custard through a fine-mesh sieve into a clean bowl for a silky finish. Pour the strained custard into the prepared pie crust.
06 - Bake for 45 to 50 minutes, or until the center is just set yet slightly wobbly. Shield the pie crust edges with foil if they brown too rapidly.
07 - Place the pie on a wire rack to cool. The custard will continue to firm up during cooling.
08 - Dust the surface with ground cinnamon and, if desired, a light sprinkling of powdered sugar. Refrigerate for at least 2 hours before slicing.