Preheat the oven to 180C/350F/Gas 4.
Grease the insides of six dariole moulds by brushing them with the softened butter.
For the cream cheese mixture, beat the cream cheese, icing sugar, lemon zest and a squeeze of lemon juice in a large bowl until well combined. Chill in the fridge until needed.
For the strawberry coulis, heat the strawberries and raspberries in a large pan for 4-5 minutes, or until they start to break down.
Add the icing (or caster) sugar and continue to cook the fruit for a further 2-3 minutes, or until the sugar has dissolved.
Transfer the coulis mixture to a food processor and blend until smooth, adding a splash of water to the mixture if necessary to loosen. Strain the coulis through a sieve and set aside to cool. Chill in the fridge until needed.
For the floating islands, make a meringue mixture: whisk the egg whites in a bowl until soft peaks form when the whisk is removed. Add the sugar and vanilla seeds and continue to whisk until stiff, glossy peaks form when the whisk is removed. Transfer the mixture to a piping bag and set aside.
For the caramel, heat a non-stick frying pan over a medium heat and add the sugar. Cook the sugar until it has dissolved and formed a caramel.
Pour a little of the caramel into each of the dariole moulds and tip the moulds to line them with the caramel.
Pipe some of the meringue mixture into each mould.
Arrange the moulds in a roasting tray. Add enough boiling water to reach halfway up the sides of the moulds and bake in the oven for 7-8 minutes, or until the meringue has just set.
To serve, drizzle a little of the coulis into each of six serving bowls. Sprinkle the raspberries, strawberries and melon into the bowls. Turn out one floating island into each bowl, spooning over any excess caramel from the mould. Place a quenelle of the cream cheese mixture alongside each serving.