For the mousse, boil the pears with lemon juice and Williams pears until soft, puree. Add gelatine while stirring with a whisk, allow to cool slightly.
Beat the egg yolks and sugar to a light, frothy mass. Stir in the pear mousse, chill until the mixture is slightly firm on the edge. Carefully fold in the egg whites and cream.
Cover and chill for 5-6 hours.
For the sauce, caramelize sugar in a chrome pan. Add water, cover and simmer over low heat until the caramel has dissolved. Add the cream, leave to cool.