Preheat oven to 120 degrees C conventional oven or 100 degrees C fan forced. Draw a 22cm circle on baking paper and place on an oven tray.
Beat egg whites with an electric mixer until soft peaks form. Add caster sugar a tablespoon at a time until meringue is stiff and shiny. This will take about 12 minutes. Add cocoa, vinegar and chocolate and lightly fold in with a metal spoon or spatula.
Spoon meringue onto baking paper to form a 22cm circle and bake for 1 1/4 hours. Turn off oven and allow to cool with oven door slightly ajar.
Place on flat serving platter. Beat cream and vanilla paste until it forms soft peaks. Spread over pavlova and top with berries.