1. Cut a piece of parchment paper to cover the bottom and sides of the jelly-roll pan.
2. Preheat oven to 190°C.
3. Beat egg whites (or the egg white powder + water mix) in a large bowl or place the egg whites in the bowl of an electric mixer and beat on high speed until stiff peaks.
4. As you whisk, add gradually white sugar a little at a time. Then add confectioners' sugar. Continue to beat more until thick and glossy. Whisk the cornflour and vinegar in.
5. Pour the meringue into the prepared pan and smooth the top. Bake for 10 mins at 190°C
degree and then reduce the heat to 160°C. Bake for another 10 to 15 mins.
6. Remove from the oven and dust with some extra confectioner's sugar onto the meringue. Turn out on to a clean piece of baking paper and peel the paper off the base. Set the meringue aside for some minutes to cool.
7. Whip the heavy cream with sugar to stiff-peaks and then add the mascarpone. Beat lightly until just combined.
8. Spread the cream evenly onto the merengue's back, spreading the cream at the far end thinner than the front. Sprinkle with raspberries pieces evenly.
9. Roll the cake on itself, holding it together with the parchment paper. Finally tighten the paper to firm it up. Wrap the paper firmly around the cake and leave it for a while. Refrigerate a few hours to set.