Prepare pie crust in a nine inch pie plate (use a flax egg to make it egg-free if desired). I’ve been using the recipe linked to in the ingredients because it’s so much less messy, but you could also use a roll-out recipe like this one.
Combine pumpkin pie spice, sugar, and cornstarch together in a sauce pan.
Add milk and stir together. The spices probably won’t mix in well until the milk gets hot, but you should stir it until the cornstarch is well incorporated.
Stir in pumpkin purée.
Heat over medium heat, stirring, until thick and bubbling.