Preheat the oven to 375°F. Lightly brush a 9-inch pie pan with vegetable oil and line it with the pie crust.
In a large bowl, whisk the eggs with butter and sugar. Add the pumpkin, milk, potato starch, orange zest, cinnamon, and vanilla. Whisk to combine. Pour the filling into the pie crust.
Place in the oven and bake for 55 minutes. If the top of the crust becomes too dark, cover the edges with a thin strip of aluminum foil.
Remove from the oven and allow the pie to cool for at least 2-3 hours before serving. Top with salted caramel sauce and whipped cream, if desired.