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.