Preheat oven to 350°F. Cook potatoes in lightly salted boiling water just until tender, about 10 minutes. Drain and set aside. Meanwhile, in medium saucepan, heat oil over low heat. Stir in flour and cook, stirring, until mixture is very thick, about 1 minute. Gradually add broth, stirring constantly. Add nutritional yeast, soy sauce, salt and pepper, stirring constantly. Remove sauce from heat and set aside.
Roll out bottom crust and fit into 9-inch pie plate. Scatter potatoes and remaining vegetables over crust and spoon sauce over them. Place top crust on pie, crimp edges and make a couple of slits in crust for steam vents. Bake until crust is lightly browned, about 1 hour. Let stand 5 to 10 minutes before serving.