As several people have asked me, here's the recipe:
2 100g bars tesco finest dark Swiss chocolate 72% (or other at least 70% choc)
6 fresh large organic free range eggs
3+ tbsp granulated sugar, to taste
Separate the eggs, beating the yolks with the sugar and the whites to stiff peaks.
Melt the chocolate in a baine-marie (or similar contraption, i.e. a heatresistant bowl over a saucepan with almost simmering water), stirring until smooth.
The next step is the only tricky bit. Stir the egg yolks into the chocolate in a constant stream very quickly so you don't end up with scrambled eggs, add a generous spoon of the egg whites and stir to loosen the mixture and then gently fold in the rest of the whites bit by bit.
Cover with clingfilm and let it set in the fridge (about 2-3 hours should do it, doing it the night before works as well).
As simple as that. :o)