Preheat the oven to 180oC. Line a 21 cm x 30 cm sponge roll pan with baking paper. Beat the egg whites, until stiff. Gradually add the sugar, beating well, until all the sugar dissolves. Fold in the vanilla, vinegar and cornflour. Spread evenly into the pan. Bake for 15 minutes, until lightly golden. Sprinkle a piece of baking paper with 2 tablespoons of icing sugar. When the meringue is cooked, turn onto the paper. Cool.
Whip the cream and the remaining icing sugar. Fold the berry puree into the cream. Spread over the pavlova. Top with a few sliced strawberries or raspberries. Roll up from the long edge, using the baking paper to help. Place on a serving dish. Dust with extra icing sugar and serve with extra berries.