01 - Preheat oven to 350°F (175°C). Fit the unbaked pie crust into a 9-inch pie pan and crimp or trim edges as desired.
02 - In a medium saucepan over medium heat, gently warm whole milk and heavy cream until steaming, not boiling. Remove from heat.
03 - In a mixing bowl, whisk together eggs, granulated sugar, cornstarch, vanilla extract, ground cinnamon, and fine sea salt until smooth and homogeneous.
04 - Slowly pour the warm milk mixture into the egg mixture, whisking constantly to temper and fully combine ingredients.
05 - Pour the custard mixture through a fine-mesh sieve into a clean bowl to ensure a silky texture, then transfer the strained custard into the prepared pie crust.
06 - Place in oven and bake for 45 to 50 minutes, until custard is set at the edges but the center remains slightly wobbly. Tent crust edges with foil if browning too quickly.
07 - Remove pie from oven and cool completely on a wire rack; the custard will continue to set as it cools.
08 - Before serving, sprinkle top with ground cinnamon and dust with powdered sugar if desired. Refrigerate for at least 2 hours before slicing and serving.