Line a baking tray with baking paper and mark a 22cm circle on paper.
Add the egg whites and sugar into the bowl of a free standing mixer and whisk on a medium/high speed for 10 minutes.
Add the cornflour, vanilla and vinegar and mix until combined
Spoon the mixture into the circle outline.
Place the pavlova into the oven and immediately turn the oven down to 100 C. Bake for 1 hour 45 minutes then turn off the oven and leave in the oven with the door closed for a further hour. After an hour, open the oven door and cool the pavlova overnight with door ajar.
When ready to serve, whip the cream with 1 tbsp icing sugar and the vanilla paste until soft peaks form. Fold in the remaining crushed Oreos and fill the pavlova with the cream.
To serve, chop the chocolate bar into shards and garnish the pavlova with the shards. Drizzle over some chocolate sauce and serve immediately.