Preheat the oven to 180C.
Beat the egg whites until really stiff. You want firm peaks that stand tall and don’t flop over when you lift the beaters.
Add the caster sugar gradually, about 1/4 cup at a time, beating on medium high until the mixture becomes thick, glossy and holds its shape. The sugar must be fully dissolved.
Turn the beaters down and add the vanilla and vinegar, then the cornflour. Beat until just combined.
Spoon the mixture into a shallow slice tray or Swiss roll tin lined with baking paper or tin foil, lightly greased underneath so it doesn’t slide. Spread it evenly with a spatula, but don’t squash the air out. Keep the thickness consistent so it rolls evenly.
Bake for exactly 12 minutes. No more. Any longer and the meringue will crisp up and you won’t be able to roll it properly. The top should be lightly golden and just set.
Remove from the oven and allow to cool. Turn out carefully onto a sheet of baking paper dusted generously with icing sugar. Gently peel off the lining paper.
Whip the cream with a teaspoon of icing sugar and a tiny splash of vanilla until softly firm. Spread over the meringue, scatter over fresh berries, then roll gently into a log. Dust with icing sugar before serving.
To freeze, leave the baking paper on, wrap well in tin foil or plastic wrap and freeze unfilled. When ready to use, unwrap and leave until it reaches room temperature. Fill and roll.

Simon Says

Use fresh egg whites if you can. Slightly older whites can whip with good volume, but your vinegar is what stabilises the meringue properly.
Your bowl and whisk must be spotlessly clean. Any grease, or even the tiniest smear of yolk, and the whites simply won’t whip. Wash in hot, soapy water and dry thoroughly before you start.
When adding the sugar, make sure it is fully dissolved. Rub a little meringue between your fingers. If it feels gritty, keep beating. It should be smooth and glossy before baking.
Don’t overfill. That’s the biggest mistake. Too much cream and berries and it slides everywhere.
Fresh berries are perfect, but pat them dry first. Any excess moisture will weep into the meringue.
Add finely grated lemon zest to the cream, or fold through a spoon of passionfruit pulp.
For a pro finish, dust the top with freeze dried raspberry powder for colour and punch. Simple upgrade, big impact.