Put the gelatine powder in a small bowl and add 2tbsp water. Leave to soak for 5 minutes.
Put the apples 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 caster sugar and whisk until stiff. Fold into the apple mixture and divide between four individual serving dishes. Chill for 1 hour until lightly set.
Meanwhile, put the Muscovado sugar, butter and remaining 30ml of cream into a shallow pan. Warm over a low heat until the sugar and butter have melted. Bring to the boil, stirring, then remove and cool.
When cool, spoon the caramel cream over the apple mousse and return to the fridge for about 30 minutes to chill.
No need to peel the apples before cooking as the mixture is puréed.
