This is a great holiday twist on those chocolate-swirled marbled cake batters we've loved for years. It's a super-quick recipe that starts with two mixes, stirs in a few clever ingredients, such as buttermilk, cocoa, and cider vinegar, and yields a terrific cake with make-from-scratch red velvet flavor. * Contributed by Catsrecipes Y-Group * Source: Southern Living 1998 Holiday Entertaining * Prep: 15 minutes | Bake: 25 minutes * Makes 1 x 3-layer cake