In the 1989 Southern classic “Steel Magnolias,” Truvy Jones, played by Dolly Parton, shared her recipe for a cuppa cuppa cuppa cake, one so simple “you don’t need to write that down.” She then explains to Clairee (played by Olympia Dukakis) that she needs just one cup of flour, sugar, and fruit cocktail—then you’ll bake until “gold and bubbly.” We tested it, and Truvy was on to something.