Preheat oven to 350˚. Spray a 13x9-inch baking dish with baking spray with flour.
In a large bowl, combine flour, sugar, baking soda, cinnamon, and salt.
In a medium saucepan, bring butter, cola, buttermilk, and cocoa to a boil over medium-high heat, whisking constantly. Remove from heat, and add to flour mixture, whisking until smooth. Add eggs and vanilla, whisking until smooth. Spoon batter into prepared pan.
Bake until a wooden pick inserted in center comes out clean, 30 to 35 minutes. Pour Cola Frosting over hot cake. Let cool for 30 minutes before serving.