Sent in by acrobat:

2 Tablespoons of Ice Cream (Vanilla or Chocolate)
1 Tablespoon of double/single cream
1 Tablespoon of sugar (can vary to taste)
1 Tablespoon of cocoa
Blend until the ice is completely mashed town into small grains.

Its really nice

There is an "Atkins" (Low Carb) version too, which goes like this:

1 Tablespoon of Splenda (its like sugar but not as naughty)
1 Tablespoon of Cocoa
2 Tablespoons of double cream (not light)

Its really nice too, although not quite as heavenly. But for people on a low carb diet, its a real treat. Its evidently not allowed in their induction though (the first 2 weeks). But after that, its allowed. (Only once per day though etc... I think its about 4 carbs or so, and you are allowed about 20 a day on Atkins).