Preheat oven to 350°.
Prepare an 8" round cake pan with a baking spray or oil and flour pan, so the cake releases easily (I use Baklene)
In a medium bowl add butter and sugar and whisk until well blended.
Add in vanilla and egg and whisk to combine.
Add in cocoa, baking soda, salt, and stir in flour
Add in buttermilk and stir,
then add in coffee and whisk until smooth.
Pour batter into prepared baking pan (wrap with a wet baking strip to bake cake evenly)
Bake at 350° for 33-35 minutes or until a toothpick comes out clean.
Remove cake from oven and allow to cool for 10 minutes then place wax paper over the top of the cake to turn cake onto a cooling rack.
Cool cake completely before applying any frosting.