Heat oven to 140 C / 120 C Fan / Gas 1. Mark a 25cm circle on baking parchment and cut this out. Place on a baking tray.
Whisk your egg whites until they form stiff peaks. Gradually whisk in the caster sugar a tablespoon at a time until the mixture is nice and glossy. Carefully stir in the cornflour, vinegar, cocoa powder and chocolate. Do not over mix. Spoon the meringue mixture onto the parchment circle.
Bake the meringue in the oven for 90 minutes, then remove and leave to cool.
Whip the double cream and icing sugar together when you are ready to serve and the pavlova is sufficiently cool. Spread the cream over the pavlova base and cover with your halved strawberries. A sprinkle of icing sugar over the strawberries gives a final flourish.