Preheat oven to 350°F (175°C). Prepare the pie crust and blind bake according to standard instructions (e.g., dock and bake for 10-15 minutes) to prevent a soggy bottom. Set the crust aside.
In a medium saucepan, combine the whole milk and heavy cream. Heat over medium heat until the mixture is steaming hot but not boiling. Remove from heat.
In a large bowl, whisk together the eggs, granulated sugar, cornstarch (or flour), salt, vanilla extract, cinnamon, and nutmeg (if using) until smooth and lump-free.
To temper the eggs, slowly and gradually drizzle the warm dairy mixture into the egg mixture while continuously whisking vigorously. This prevents the eggs from scrambling. Pour the entire tempered mixture back into the saucepan.
Cook the custard mixture over low heat, stirring constantly, until the custard thickens slightly and coats the back of a spoon. Do not allow it to boil.
Pour the finished custard filling into the prepared pre-baked pie crust. Carefully place the pie back into the preheated oven.
Bake for 30–50 minutes, or until the edges are set but the center of the custard still has a slight, controlled wobble. The internal temperature should reach 175°F (80°C).
Remove the pie from the oven and allow it to cool completely on a wire rack at room temperature. Once cooled, refrigerate for at least 2 to 4 hours (or ideally overnight) until the custard is fully set.
Serve chilled. Garnish with a dusting of cinnamon and fresh whipped cream for optimum festive cheer.