Mix first five ingredients. Beat egg. Add to buttermilk, oil and vanilla. Add egg mixture and hot coffee to flour mixture and stir gently as batter will be thin. Bake at 350 degrees for 30-40 minutes until done.
To prepare Penuche Frosting: Mix all ingredients except vanilla in a pan and bring to a slow boil stirring constantly. Boil one minute. Cool to lukewarm. Add vanilla. Beat with mixer until spreadable. If you desire, melt dark chocolate chips and drizzle over Penuche Frosting.