Craft the Perfect Crust: In a large bowl, whisk your flour, salt, and sugar. Cut in the cold vegan butter using a pastry cutter until it looks like coarse crumbs. Slowly add ice water until the dough holds together. Divide into two balls, flatten slightly, wrap, and refrigerate for at least one hour. Once chilled, roll out to 1/8-inch thickness and fit into your pie plates.
Blend the Filling: Preheat your oven to 350°F. Place your mashed potatoes, squash, sugars, spices, vanilla, milk, and arrowroot powder into a blender or food processor. Blend until it’s perfectly smooth and creamy.
Bake to Perfection: Divide the filling between your two crusts. Bake for 50 minutes. You’re looking for the center to be set—it shouldn’t jiggle when you move the pan.
The Chill Factor: Let the pies cool on a wire rack for 30 minutes, then move them to the fridge for a few hours (or overnight). This allows the filling to firm up for those perfect, clean slices.