Preheat the oven to 150°C and line a large baking tray with non-stick baking paper.
Whisk egg whites on high speed, adding 300g sugar gradually until smooth and glossy.
Reduce speed to incorporate cornflour and vinegar, then whisk on high until stiff peaks form.
Use small dabs of meringue to secure the baking parchment to the tray.
Spread meringue in a large circle and bake at 150°C for 10 minutes, then at 100°C for three hours.
Melt white chocolate in a heatproof bowl over a pan of simmering water.
Whisk double cream to soft peaks, then fold in custard and whisk again to soft peaks.
Heat 200g sugar in a saucepan until it turns into a golden-brown liquid caramel.
Spread melted chocolate over the cooled meringue followed by the cream mixture.
Top with fresh raspberries and drizzle with the prepared caramel.