Grease and flour a 9-inch round cake pan, 3 inches deep.
In a saucepan, combine the butter, water, and coffee over medium heat until they come to a slow boil.
Remove from the heat and add the chocolate, stirring until it’s completely melted.
Set aside to cool to room temperature.
In a large bowl, whisk together the flour, sugar, cocoa, baking powder, and baking soda and make a well in the center.
Pour in the eggs, buttermilk, oil, and chocolate mixture and stir vigorously with a wooden spoon until there are no lumps.
Pour into the prepared pan and bake until a skewer inserted in the center comes out clean, about 1 hour and 15 minutes. Allow the cake to completely cool in the pan before removing.