Preheat oven to 180°C/160°C fan forced. Grease two 20cm springform pans and line base and sides with baking paper. Grease the paper and sprinkle with cornflour, shaking away excess.
Using electric beaters, beat egg whites in small bowl until soft peaks form. Gradually add sugar, beating after each addition until sugar is dissolved. Fold in hazelnut meal, vinegar and extract.
Divide meringue mixture evenly between pans. Bake for 35 minutes or until meringue is crisp. Release sides of pans and cool meringues on bases.
Combine chocolate and butter in small bowl.
Remove meringue from bases. Place one layer on a plate, flat-side down. Spread with half the chocolate mixture and top with half the cream and strawberries.
Spread flat side of second meringue layer with remaining chocolate mixture. Place on top of strawberry layer, chocolate side down. Spread remaining cream over top of cake. Refrigerate for 3 hours or overnight. Dust with cocoa powder.