Put the gelatine powder in a small bowl and add 2tbsp water. Leave to soak for 5 minutes.
Put the pears in a saucepan with 25g of the caster sugar and 30ml water. Cook gently, stirring, for about 10-15 minutes until very soft. Stir the soaked gelatine into the warm mixture then purée in a blender. Leave to cool.
Stir 300ml of the double cream into the cooled purée mixture and chill for 10-15 minutes until just beginning to set.
Whisk the egg white to soft peaks, add the remaining sugar and whisk until stiff. Fold into the pear mixture and divide between four individual serving dishes. Chill for 1 hour until lightly set.
Meanwhile, put the chopped chocolate in a small bowl. Heat the remaining cream until almost boiling and pour over the chocolate. Stir until melted and smooth.
When cool, spoon the chocolate cream over the pear mousse and return to the fridge for about 30 minutes to chill.
No need to peel the pears before cooking as the mixture is puréed.
