Guiness Slammer recipe

I was introduced to this lovely concoction at a tavern in charolette N.C. A newly aquired freind took me to his favorite neighborhood watering hole called the Thomas Street Tavern. I orderd a Guiness draught. He seeing this made a "B" line to the bartender and brought back this very different looking pint glass, then after teilling me this was the bartenders favorite and most of the patrons also ,he coaxed me in downing the drink. Upon bringing the empty glass from my lips , I quickly ordered another. I hope you enjoy this slammer as much as I do.