Use white vinegar or lemon juice to wipe down the mixing bowl, whisk attachment and spatula that you will be using. Grease is meringue’s enemy and you want to ensure your equipment is grease free.
Preheat the oven to 300°F. Use an 8 or 9-inch guide to trace a circle on a piece of parchment paper. Place the paper, pencil side down, on a baking sheet pan and set aside.
In the bowl of a stand mixer, add the egg whites and kosher salt. Mix on medium-low until they become frothy, about 2-3 minutes. Then add the vinegar.
Now add the superfine sugar, one tablespoon at a time, lightly sprinkling it into the beating egg whites. It should take about 15 seconds of sprinkling per tablespoon; wait a few seconds after one tablespoon has been added before adding the next. (you want to add the sugar slowly to allow it to dissolve easier).
Once all the sugar has been added, stop the mixer and scrape the bowl. Then add the vanilla and beat on medium-high until the mixture becomes glossy and stiff peaks are formed, about 5-7 minutes.
Then sift the cornstarch over the meringue and fold it in with a spatula.
Use the spatula or a spoon to move the meringue to the middle of the drawn circle on the parchment paper. Gently spread the meringue into the shape of a circle, using the drawn lines as a guide. Make a slight depression in the middle. If desired, you can lightly drag the spatula/spoon up the sides to create a pattern along the sides.
Place in the oven and REDUCE the temperature to 225°F bake for 2 - 2 ½** hours or until the meringue is slightly creamy in color and feels dry on the outside. (You can start checking for doneness at the 2 hour mark).
Turn the oven off and leave the pavlova in the oven to cool completely, at least 3 hours. It can be left for multiple hours or overnight.
When ready to serve, make the whip cream by combining the heavy whipping cream and sugar in a bowl and beat with a hand or stand mixer until medium-stiff peaks.
Carefully move the pavlova to a serving plate. Spoon the whipped cream over the top and gently add the fruit to decorate, garnish with mint or a dusting of powdered sugar, if desired. Serve immediately.