Preheat the oven to 200 (F). Prepare a large baking sheet by lining with parchment paper.
In a small bowl, whisk together 1 cup granulated sugar and 1 tablespoon cornstarch. Set aside.
In the bowl of a freestanding electric mixer fitted with a whisk attachment, whisk together 4 egg whites, 1 teaspoon lemon juice, and 1/4 teaspoon kosher salt on low speed until very frothy. When the mixture is frothy, increase mixer speed to medium-high and gradually add the sugar and cornstarch mixture (from the second step), beating until stiff, glossy peaks form, about 12 to 15 minutes. Be sure to scrape down the sides of the bowl with a rubber spatula halfway through the mixing process.
When the mixture is glossy and stiff, use a rubber spatula to mound onto the center of your prepared parchment sheet. Use the rubber spatula to spread the mound until it is a 7-inch circle, and create a well 3 1/2-inches wide and 1-inch deep in the center of the mound. Transfer to the preheated oven and bake for 2 1/2 hours, or until the mound is crisp on the outside and soft inside.
When the pavlova is ready, turn off the oven heat and let the pavlova cool in the oven for at least 2 1/2 hours, or until completely cool (preferably overnight).