Preheat oven to 350 degrees and lime a baking sheet with parchment paper. Draw a 9 inch circle on the paper and flip paper over so you can still see the outline of the circle.
Beat egg whites until satiny peaks form, then add the cream of tartar and the sugar, one spoonful at a time, and continue beating until meringue is soft and shiny.
Sprinkle the cocoa, vinegar and then the chopped chocolate, gently folding everything with a rubber spatula until cocoa is thoroughly incorporated.
Mound meringue onto a parchment paper lined baking sheet within the circle, smoothing the sides and top with the spatula.
Place in oven and lower temperature to 300 degrees, cooking for 1 1/2 hours*. The pavlova should look crisp and dry on the top but the center should be squidgy.
Turn off the oven and open the door slightly allowing the meringue disc to cool completely in the oven.
When ready to serve invert meringue onto a flat-bottomed plate and peel off parchment.
Whip the cream until thick but still soft, add the confectioner's sugar and vanilla and whip a bit more. Pile on top of the completely cooled meringue. Carefully sift the cocoa on top of the whipped cream. Scatter the berries or place decoratively and coarsely grate chocolate over the top so you get chocolate curls.
Cut into eight wedges and celebrate with friends and family.
*Keep in mind that if you live in a humid environment, the cooking time of the pavlova may vary. I ended up cooking my pavlova for almost 2 1/2 hours.