Warm the jam slightly and brush it over the sides of a 15 cm/6 in
springform cake tin (pan). Trim the ends of the sponge fingers and stand
them round the edge. Whisk the egg whites until very stiff. Whisk together
the egg yolks, icing sugar, coffee essence and rum, then fold in the egg
whites and double cream. Spoon the mixture into the cake tin and freeze
for 5 hours. When ready to serve, carefully loosen round the side of the
tin with a palette knife and turn out. Decorate with whirls of whipped
cream and sprinkle the grated chocolate over.