Add the egg whites, sugar, cornstarch, vinegar and vanilla to a grease-free mixing bowl.
Beat on high until eggs are fluffy and doubled in volume.
Add boiling water all at once.
Continue to beat on high until stiff glossy peaks are formed.
Spread on a baking sheet lined with parchment paper. Smooth out into a 9x13 inch oval.
Place in oven. Close the door.
Immediately reduce oven temperature to 200℉, continue to bake for 60 to 90 minutes.
Without opening the door, turn oven off and let the pavlova sit in the oven for 1 hour, until completely cooled.
Whip one small carton of heavy whipping cream until stiff peaks form.
Spread over the top of the pavlova.
Add fresh berries and serve immediately.
Special Equipment:Stand Mixer | Hand Mixer | Parchment Paper | Piping Bag | Piping TipAcid: If you don't have white vinegar you can substitute Apple Cider Vinegar or even lemon juice. Alternatively, ½ teaspoon of cream of tartar will also work to stiffen the egg white mixture. Chocolate Pavlova: Add three tablespoons of sifted unsweetened cocoa and 2 ounces of finely chopped bittersweet chocolate to the egg mixture.