Preheat oven to 400 degrees F and grease a 10x15" sheet pan (I like to line mine with tin foil before greasing!).
In a large bowl, combine butter and sugar with a whisk. Add eggs and whisk until smooth.
Add cocoa, milk, baking soda and vanilla and whisk until combined.
Stir in flour. Add coffee and stir until combined.
Spread into prepared baking sheet and and bake for 20 minutes, turning half way. Remove from the oven and cool to room temperature.
FrostingIn a medium bowl, combine butter, cocoa, milk, sugar and vanilla and whisk until combined. Spread over cooled brownies and let set -- or don't! Simply cut yourself a slab and dive right in ?