First, melt the chocolate and butter together and whisk to combine. In a separate bowl whisk the eggs and sugar until they are pale and fluffy (it's easier to with an electric mixer). Add flour to the egg mixture and combine. , then fold the chocolate mixture into the egg mixture.
Beat rigorously to remove the excess air from the mix and pour into a piping bag or a jug.
Line some metal rings 10cm in diameter and 5cm height with butter and greaseproof paper and pipe the mix to just below the top of the ring.
Bake in the oven at 200°C for six minutes, then remove and allow to sit for a minute. Remove the ring dust with icing sugar if desired and serve with a good quality ice cream.