Preheat oven to 350°F Grease two 8 inch pans and line the bottoms with waxed paper.
Whisk the egg whites in a large bowl until they hold stiff peaks, then gradually whisk in the superfine sugar one tablespoon at a time, whisking after each addition.
Continue whisking the meringue for 1-2 minutes, until very stiff, then fold in the vanilla extract, vinegar and ground hazelnuts.
Divide the meringue mixture between the prepared cake pans and spread level. Bake for 50-60 minutes, until crisp. Remove the meringues from the pans and let them cool on wire racks.
While the meringues are cooling, make the sauce. Process the raspberries with the confectioner's sugar and orange liqueur in a blender or food processor, then press the puree through a fine sieve to remove any seeds. Chill the sauce until ready to serve.
Whip the cream until it forms soft peaks, then gently fold in the raspberries. Sandwich the meringue rounds together with the raspberry cream.
Dust the top of the gateau with confectioner's sugar. Decorate with mint sprigs and serve with the raspberry sauce.