Preheat oven to 375°F (190°C). Roll out the pie crust to fit a 9-inch dish, line with parchment, and fill with weights. Bake for 20 minutes until slightly golden, then cool.

In a medium saucepan, combine whole milk, heavy cream, cinnamon, and vanilla. Heat over medium until steaming, then remove from heat.

In a large bowl, whisk eggs, sugar, and salt until pale and frothy, about 2-3 minutes.

Gradually pour the warm milk mixture into the egg mixture while whisking to prevent scrambling. Strain through a sieve into a clean bowl.

Reduce oven to 325°F (160°C). Pour the custard into the pre-baked crust. Bake for 35-40 minutes until edges are set but center jiggles.

Cool the pie at room temperature for 30 minutes, then refrigerate for at least 2 hours before serving.