Grease a 15 cm (6 in) cake tin with a detachable base
Break up the chocolate and put it in a bowl over a saucepan of simmering water to melt
Melt the butter gently in another pan
Beat the eggs and sugar in another bowl, pour in the melted butter in steady stream beating continuously
Now blend in the melted chocolate and break up the biscuits into pieces and fold them into the chocolate
Turn the mixture into the cake tin and chill overnight, in the refrigerator
To serve stand the cake tin on a canister at least 5 cm (2 in) smaller than the base of the tin
Push the tin carefully down on to the table, leaving the base with the cake on the canister
Slide it on to a serving plate and decorate with Cadbury gems and Oreo cookies cut in half