1. Place half the blackberries in a thick-bottomed saucepan over a gentle heat and stir until softened. Stir in 2 teaspoons of honey.
2. Remove from the heat, add the lemon juice and sprinkle in the gelatine, stirring well to dissolve. Push through a sieve then leave the mixture to cool and thicken.
3. Combine the yogurt and Petit Suisse cheeses and stir in the cooled blackberry puree.
4. Whip the egg whites until stiff and fold in.
5. Reserve a few blackberries for decoration. Divide the remainder between 6 tall wineglasses and pour 1 tablespoon of port into each. Top up with mousse mixture and chill.
6. Just before serving, dry-fry the hazelnuts with the lemon rind. When evenly coloured chop them and sprinkle a little over each glass. Decorate with the remaining berries and honey.