Heat the vegan butter (or oil) in a large pot and cook the veggies (garlic, onion, celery, and carrots) over medium-high heat for about 10 minutes or until soft, stirring occasionally.
Add the vegan chicken and cook for 3-5 more minutes, stirring frequently.
Add the flour and cook for 1 to 2 minutes, stirring constantly.
Then add the vegetable stock and the plant milk and stir. After that, incorporate all the remaining ingredients, stir again and cook until it thickens, stirring occasionally.
Remove from the stove and set aside.
In the meantime, make your vegan pie crust. You’re going to need 2 disks of vegan pie crust. If you’re going to use a store-bought version, omit this step.
Pour the filling into the pie crust-lined pan. I use a 9-inch or 23 cm round pie pan.
Roll the second vegan pie crust into a round and place over the pie filling. Fold the excess dough behind the bottom crust then crimp the pie crusts together to seal.
Cut a few slits in the middle of the top crust to allow steam to escape. Brush the top of the crust with melted vegan butter (you could also use oil or plant milk, but I think vegan butter is the best choice).
Bake for 35 to 45 minutes or until the top crust is golden brown. Remove from the oven and let it rest for 15 minutes to cool slightly before slicing.