Put the butter, cocoa powder, and soda in a small saucepan. Whisk it together, place it on medium heat, and bring it to a boil. Make sure to keep whisking.
1 cup salted butter, 6 tablespoons baking cocoa, 1 cup Coca-Cola
Once it starts boiling, take mixture off heat and pour it into bowl with the flour mixture.
Stir everything together until it's thoroughly combined.
Add the vanilla, buttermilk, and eggs to the mixture, stirring until it's well mixed.
2 eggs, 1 teaspoon vanilla extract, 1/2 cup buttermilk
Pour the cake batter into the prepared baking pan.
Bake in the preheated oven for 30 minutes. The cake is done when a toothpick inserted into the center of the cake comes out clean.
When you remove the cake from the oven, start on your frosting. Put the butter, cocoa powder, vanilla extract, and Coca-Cola in a medium saucepan. Mix and bring it to a boil, stirring constantly.