Have not tried this yet but sounds tasty.
place 4 scoops of vanilla ice cream in a blender, let soften first for about ten minutes.
add 12 ounces of Guinness ( Draught or Stout as preferred) pour slowly to avoid too much foam.
blend until smooth. If too watery add more ice cream, if too thick add more Guinness.
pour into serving glasses, this make about 2 16 ounce drinks.
enjoy.