Line the pie crust with foil or parchment paper and fill with pie weights or dry beans. Bake for 10 minutes. Remove pie weights and foil and bake for another 5-7 minutes. Turn oven temperature down to 375°
While crust is baking, prepare custard filling. Whisk together sugar and cornstarch in a heavy saucepan. Gradually whisk in the milk till cornstarch is dissolved.
Heat over medium heat, stirring constantly, till mixture comes to a boil. Whisk and stir for another minute or two, until thick.
Remove from heat and add vanilla and butter. Stir till butter is melted; pour into partially baked pie shell. Sprinkle with cinnamon sugar mixture.
Bake at 375° for another 15-20 minutes, or until filling starts to bubble. Remove to a cooling rack to cool. Chill for 3-4 hours.
Notes
-A deep dish pie crust works best for this recipe. You can use a refrigerated pie crust or make your own.