Preheat the oven to 375°F (190°C). Roll out the pie crust into a 9-inch pie dish and line it with parchment paper. Fill with weights and bake for 15 minutes. Remove weights and bake for an additional 5 minutes.

Combine whole milk and heavy cream with ground cinnamon and pure vanilla extract in a saucepan. Heat gently until steaming, then steep a cinnamon stick or split vanilla bean for 10 minutes if desired.

In a large bowl, whisk together eggs, granulated sugar, and salt until smooth and pale.

Slowly pour the hot milk mixture into the egg mixture while whisking constantly to prevent curdling. Strain the mixture through a sieve to remove lumps.

Lower the oven temperature to 325°F (160°C). Pour the custard into the crust and bake for 35-40 minutes until the edges are set and the center jiggles slightly.

Cool the pie to room temperature on a rack, then cover loosely and refrigerate for at least 2 hours to set.