Line a baking sheet with parchment paper. Tip: trace circles onto parchment using a yogurt or tupperware lid to ensure all pavlovas are the same size. I used a 5" lid to trace 8 circles.
Preheat over to 350° F (oven will be immediately turned down once you put pavlova in).
Combine sugar, cornstarch, and salt in a small bowl and set aside.
In a large bowl, whip the egg whites using an electric mixer until soft peaks form. Gradually add the sugar mixture, one tablespoon at a time, while continuing to whip. Once all the sugar mixture is added, continue whipping until mixture has stiff, shiny peaks. Very gently fold in vanilla and fresh lemon juice.
Add meringue mixture to a piping bag fitted with a large star tip. Pipe meringue onto parchment paper, moving in a circular direction. First pipe a bottom layer, then continue piping on top of that layer, leaving a well in the center that can be filled after baking.
Place in oven and immediately turn heat down to 225° F. Allow pavlova to bake until dry, about 1 1/2 hours. Turn off heat and leave in oven to cool completely, about an hour.