Preheat oven to 350º F and grease and lightly flour a 9x13" casserole dish.
Put the flour, sugar, cocoa, baking powder, baking soda and salt in a large bowl. Whisk together until combined.
In a separate bowl, put the buttermilk, vegetable oil, eggs and vanilla extract and use an electric mixer to blend together.
Pour the wet mixture into the dry and use your mixer to blend until combined. With the mixer running, add the hot coffee and mix on high speed for about 1 - 2 minutes.
Pour the batter into the prepared pan, and bake for about 35 - 40 minutes, or until a toothpick test comes back clean.
Allow to cool for about 10 minutes in the pan, then remove from the pan and allow to cool completely.
for the icing:
Use your electric mixer to cream together the butter and cocoa powder. Add the milk and powdered sugar in 3 separate additions, blending until combined, then mix in the vanilla.
If the frosting is too dry, you can add a tablespoon of milk at a time until it reaches the perfect consistency. If it's too wet, you can add a little more powdered sugar at a time until it reaches the perfect thickness.
When the cake is completely cooled, use a large serrated knife to cut in in half horizontally.
Drain the can of cherry pie filling in a strainer, and shake it a bit to remove most of the juice. Spread a thin layer of icing over the top of the inside layer of the cake, then spread the drained cherries on top. Replace the top layer of the cake and spread the remaining icing across the top and sides.