Preheat oven to 350°. Grease a 13x9-in. baking pan.
In a large bowl, whisk the first 5 ingredients. In a small saucepan, combine cola, butter and cocoa; bring just to a boil, stirring occasionally. Add to flour mixture, stirring just until moistened.
In a small bowl, whisk eggs, buttermilk and vanilla until blended; add to flour mixture, whisking constantly.
Transfer to prepared pan. Bake 25-30 minutes or until a toothpick inserted in center comes out clean.
About 15 minutes before cake is done, prepare glaze. In a small saucepan, bring cola to a boil; cook 12-15 minutes or until liquid is reduced to 1/2 cup. Stir in butter and cocoa until butter is melted; remove from heat. Add confectioners' sugar; stir until smooth. Pour immediately over hot cake.
Coca-Cola Cake Tips
What does adding soda to cake do?
In addition to being a time-saver, the carbonation in soda gives a boxed cake mix extra lift and lightness when baked. Adding soda also results in a cake that’s lower in fat without the addition of eggs and oil that most cake mixes call for. And cakes aren't the only dish that can benefit from a little soda—some meat recipes, like these cola burgers, also call for it.
What does Coca-Cola cake taste like?
The cola imparts such a subtle flavor that you’ll be hard-pressed to identify it. The acid in the soda balances out the cake's sweetness. Colas pair well with chocolate cake mixes—you can also use root beer, cherry cola or Dr. Pepper. White sodas work best with white, vanilla, orange and lemon cakes and desserts. For example, these Pumpkin Doughnut Drops have lemon-lime soda.
Can you bake with diet soda?
You can substitute diet cola for full-sugar soda with good results in cakes. However, for the best flavor, look for one without artificial sweeteners.
Research contributed by Catherine Ward, Taste of Home Prep Kitchen Manager