Step 1: Preheat oven to 375°F (190°C). If using a homemade pie crust, blind bake it for 10-15 minutes until lightly golden. Let cool slightly.
Step 2: In a large bowl, whisk together eggs, sugar, cinnamon, and salt until well combined.
Step 3: In a separate saucepan, gently heat the milk over medium heat until small bubbles form around the edges (do not boil).
Step 4: Gradually temper the egg mixture by slowly whisking about half of the warm milk into the egg mixture. This prevents the eggs from scrambling.
Step 5: Pour the tempered egg mixture back into the saucepan with the remaining warm milk. Whisk continuously over low heat for 5-7 minutes, until the custard thickens slightly and coats the back of a spoon. Do not boil.
Step 6: Remove from heat and stir in the vanilla extract.
Step 7: Pour the custard filling into the cooled pie crust.
Step 8: Carefully transfer the pie to the preheated oven. Bake for 35-45 minutes, or until the edges are set but the center still jiggles slightly when gently shaken. A knife inserted near the edge should come out clean.
Step 9: Remove from oven and let cool completely on a wire rack before refrigerating for at least 3-4 hours, or until thoroughly chilled and set.
Step 10: Garnish with a pinch of freshly grated nutmeg, if desired, before serving.