Preheat your oven to 375°F (190°C). Roll your pie crust into a 9-inch pie dish and ensure it's well-fitted. Line with parchment paper, then fill with pie weights or dried beans. Bake for 15 minutes, then carefully remove the weights and parchment, and bake for another 5 minutes until the crust is golden and slightly crisp. Let it cool slightly on a wire rack.

In a medium saucepan, combine whole milk and heavy cream with ground cinnamon and vanilla extract. Heat this mixture over medium heat until steaming, stirring gently but do not let it boil. If using a cinnamon stick or vanilla bean, steep for 10 minutes to infuse flavors before removing.

While your milk mixture is heating, crack the room-temperature eggs into a large mixing bowl. Add granulated sugar and a pinch of salt. Whisk vigorously until pale and smooth, about 2-3 minutes.

Gradually add the hot milk mixture to the egg mixture while whisking continuously to prevent curdling. Strain the mixture through a fine mesh sieve into a clean bowl.

Lower your oven temperature to 325°F (160°C). Carefully pour the custard mixture into the pre-baked crust. Bake for 35-40 minutes or until the edges are set, but the center jiggles slightly.

Once baked, let it cool to room temperature. Refrigerate for at least 2 hours to set the custard fully.