Melt chocolate with a little water
Add remaining water & sugar and heat gently, stirring, to dissolve the sugar
Simmer for 10-15 minutes until the mixture thickens & leave to cool
Whip the cream and fold in 3 tablespoons of the cooled sauce
Spread onto one of the hazelnut meringue disks and top with the other
Chill overnight before serving with the remaining chocolate sauce