Break the chocolate into rough chunks.
Heat the cream in a pan over a low heat until almost boiling then add the chocolate and remove from the heat.
Cover the pan for about 5 minutes, then add the vanilla essence to the mixture and begin stirring until smooth.
Pour the mixture into a large bowl and chill until it begins to thicken.
Line a 450 g - 1 lb loaf tin with cling film overlapping the edges of the tin.
Spread 1/6 th of the chocolate mixture over the base of the tin.
Cover with a layer of biscuits then repeat in this fashion until the last layer is of the chocolate.
Cover with the cling film then chill for a few hours until the chocolate has set firmly.
Unwrap the cling film from the top of the cake and turn out onto a serving plate.
Carefully peel of the cling film and slice thinly and serve.