Melt the butter in a casserole.
Add the chocolate and stir until melted. Let cool for 15 minutes.
Whip the eggs and icing sugar together.
Mix the chocolate and the icing sugar mixture together.
Cover a long baking form with plastic foil.
Cover the bottom with some biscuits. Add some chocolate so it covers the biscuits. Repeat and end with chocolate.
Place in the fridge over the night.
Cut the cake in thin slices before serving.