Preheat oven at 225˚ F.
Place parchment paper on a baking sheet, and trace 2 (6-8 inch circles).
Using a stand mixer, whisk the egg whites until soft peaks form. Slowly add in the sugar; continue whisking (8-10 minutes), until egg whites become stiff and the mixture is smooth and glossy.
Combine cornstarch, vinegar, and vanilla in a small bowl; gently fold into the meringue mixture, until fully incorporated but do not over mix, about 5-6 seconds.
Flip parchment paper over (traced circles should be facing down towards the sheet pan). Spoon or pipe the meringue in the middle of each circle, then use a spoon to push outwards; creating a well with the meringue for the filling. Bake for 1 hour and 30 minutes. Turn oven off and without opening the door; let meringue sit in the oven for 2-3 hours or up to 8 hours (the longer it sits the crispier the shell). Do not skip this step!
The outside will be dry and crisp and the inside will still be marshmallow soft.
Store pavlova shells at room temperature, in an airtight container for 3-5 days until ready to fill. Right before serving, top one shell with cream, and then stack the second shell on top. Cover with remaining cream and macerated berries. Enjoy!
Lemon Whipped Cream:
Place bowl, whisk and cream in the freezer for 5-10 minutes.
Combine all ingredients in a medium bowl. Using an electric mixer, beat to soft peaks.
Use immediately or cover tightly and chill in the refrigerator for up to 2 hours. If stored overnight, the cream will have to be re-whipped before serving.
Combine berries with sugar and juice in a large bowl until sugar begins to dissolve.
Let the mixture sit at room temperature, tossing occasionally, until berries are juicy, 1-2 hours.