Melt the chocolate and butter or
margarine in a heatproof bowl set over a pan of gently simmering
water. Remove from the heat and stir in the sugar until dissolved,
then beat in the eggs and cornflour. Spoon into a greased and lined 20
cm/8 in cake tin (pan) and stand the tin in a roasting tray containing
enough hot water to come half-way up the sides of the tin. Bake in a
preheated oven at 180ºC/350ºF/gas mark 4 for 1 hour.
Remove from the tray of water and leave
to cool in the tin, then chill until ready to turn out and serve.