Preheat oven to 350°F. Grease a 13x9-inch baking dish with butter or nonstick cooking spray.
In a large mixing bowl, whisk together flour, granulated sugar, and baking soda.
In a saucepan over medium heat, combine Coca-Cola, oil, salted butter, and cocoa powder. Stir until the butter is melted and mixture is smooth. Once it starts to come to a boil, remove from heat.
Pour the warm Coca-Cola mixture into the flour mixture. Mix with a hand mixer or whisk until smooth and free of lumps.
Add buttermilk, and blend for 30 seconds.
Add eggs and vanilla extract. Blend another 30 seconds.
Pour the batter into the prepared pan and smooth the top with a spatula. Bake for 30-35 minutes or until a toothpick inserted in the center comes out clean. Allow the cake to cool in the pan before adding the frosting.