I used:
About 1/3 pint of milk (use soya, almond or coconut if you don't want to use normal milk. I've tried it with soya and that's great)
3 teaspoons of cream
Handful of mint leaves (can also used dried mint, even peppermint extract!)

Heat this in a pan, and leave to infuse for half an hour.

In a separate bowl, beat an egg (can use just egg yolk, or whole egg) with splenda (as much as you like, I use roughly 5 tablespoons).
Add one spoonful of the milk mixture to the egg, and stir. Then another spoonful, stir. And again. (This is to temper the egg).
Sieve the rest of the milk mixture into your egg, to get rid of the leaves, and squeeze them down to get all the mintyness out of them.
Then heat this, very very slowly, whilst keeping on stirring, until it thickens. (If you draw a line with your finger down the back of the spoon, the mixture should not leak back into the line)
Refridgerate this, then when it is cool, finely chop in a couple of squares of chocolate (I use Cavalier Extra dark).
Taste it aswell to check sweetness!
I then put it in my icecream machine for 25 mins, and for me this is one serving (but a very large one, so really it could serve 2).