How to Make the Cake:
Preheat oven to 375ºF (190ºC) and grease two 9-inch cake pans with butter or non-stick spray.
In a large bowl, whisk together the flour, sugar, cocoa powder, baking soda, and salt.
Add the water, oil, apple cider vinegar, coffee (if using), and vanilla extract.
Stir until smooth and no lumps remain.
Pour batter evenly into the prepared cake pans.
Bake for 24–26 minutes, or until a toothpick inserted in the center comes out clean.
Remove from oven and let cool completely before frosting.
How to Make the Frosting:
In a bowl or mixer, whisk together the powdered sugar, cocoa powder, and salt (if using).
Add the water, softened butter, and vanilla extract.
Beat until the frosting is smooth and creamy.
Add more powdered sugar to thicken or more water to thin, if needed.
Once the cake is cooled, spread frosting evenly over the top.
