Pre-heat the oven to 225 degrees. Line two baking sheets with parchment paper or silicone baking pads (Silpat). To make the meringues, combine 1/4 cup of the sugar with the cornstarch in a small bowl and set aside. Whip the egg whites and salt using a standing mixer fitted with a whisk attachment (or a hand mixer). Start on low speed unil the eggs start to foam and then increase the speed to high. As the eggs start to turn white and come together add the remaining 1 cup of sugar, 1 tablespoon at a time. Continue to beat the eggs until they become stiff and shiny. You are looking for stiff peaks.
Remove the bowl from the machine and add the vanilla and vinegar by hand, folding in these ingredients gently with a rubber spatula. Sift the sugar/cornstarch mixture over the whipped egg whites and fold this in as well. Spoon the meringue onto the baking sheets – about a half a cup of the batter per pavlova. Using a large spoon spread out the batter leaving a depression in the center for the topping. Bake the meringues for 60-75 minutes or until they are dry. Turn off the oven and let them continue to dry out for several hours.
In the bowl of a standing mixer, combine the heavy cream, powdered sugar and vanilla. Using the whisk attachment, beat the cream until stiff peaks form. Top the cooled meringues with whipped cream and fresh strawberries.