Preheat your oven to 350°F (175°C) and grease a 9x13-inch baking pan thoroughly with butter or non-stick spray.

In a large mixing bowl, whisk together the flour, sugar, and salt.

In a saucepan, combine the butter, cocoa powder, and Coca-Cola, stirring over medium heat until boiling. Remove from heat.

Pour the warm cocoa mixture over the dry ingredients and stir until just combined.

Add the beaten eggs, buttermilk, baking soda, and vanilla extract to the batter, mixing until smooth.

Pour the batter into the prepared baking pan and bake for 30-35 minutes, or until a toothpick comes out clean.

While the cake is baking, melt the butter for the frosting in a saucepan, then add Coca-Cola and cocoa powder, bringing to a gentle boil.

Gradually whisk in powdered sugar until smooth, then add vanilla.

Pour the warm frosting over the hot cake immediately after it comes out of the oven.

Allow the cake to cool for at least 20 minutes before slicing.