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.