In A 12 In. Nonstick Skillet, Melt Butter; Remove From The Heat. Arrange Potatoes On The Bottom And Up The Sides Of Skillet; Sprinkle With Onion, Salt And Pepper. Cover And Cook Over Low Heat Until The Potatoes Are Tender, About 20 Minutes. Sprinkle With Cheese; Layer With Half Of The Tomato Sauce, All Of The Pepperoni And Tomatoes, And The Remaining Tomato Sauce. Cover And Cook On Low Until The Cheese Is Melted And The Tomatoes Are Heated Through.