one cup of sugar
one cup of self-raising flour
2 eggs
3 tea spoonfuls of plain yoghurt
200g dark chocolate
50g butter (or margarine)

Mix together the eggs and sugar until the mixture gets white and creamy; stir in the melted butter. Add the flour and yoghurt. Melt the chocolate in a pan (bain-marie) with a tiny bit milk or cream to make it easier.
Add the melted chocolate to the mixture. Butter a (foiled) tin, pour in the mixture.
Pre-heat the oven for 10 mins. Our oven is crap, we can't really regulate the temperature and it overheats from the bottom, so you'll have to check the cake regularly with a knife. It should bake for about 40 mins.