Preheat your oven to 375°F (190°C) while you prepare your pie crust. If you're using a homemade crust, roll it out and carefully place it in a 9-inch pie dish. Blind-bake for 15 minutes with parchment paper and weights, then remove weights and bake for an additional 5 minutes until golden brown. Set aside to cool.

In a medium saucepan, combine whole milk and heavy cream with ground cinnamon and pure vanilla extract. Heat gently over medium until steaming but not boiling. If using whole spices, allow them to steep for a few minutes. Remove from heat and let cool slightly.

While the milk mixture cools, whisk together eggs, granulated sugar, and a pinch of salt in a separate bowl until pale and slightly thickened.

Gradually incorporate the warm milk mixture into the egg mixture, whisking to prevent curdling. Pour through a fine mesh strainer for a smooth custard.

Pour custard filling into the pre-baked crust, spread evenly. Lower oven temperature to 325°F (160°C) and bake for 35-40 minutes or until edges are set and center has a slight jiggle.

Remove pie from the oven and cool at room temperature for about an hour. Then cover and refrigerate for at least two hours to let the custard set.