Preparation

• 位置的中心架the oven, and heat the oven to 275°F. Coat a baking sheet with cooking spray and line with parchment. Draw a 9-inch circle in the center of the parchment, then turn the paper over (you’ll still see the circle).
• Combine 2 tsp. of the sugar with the potato starch in a small bowl and set aside.
• In the bowl of a stand mixer fitted with the whisk attachment (or in a large bowl using a hand-held electric mixer), beat the egg whites with the lemon juice and salt on medium-high speed until soft peaks form, about 2 minutes. With the mixer running, slowly add the remaining 1 cup sugar, about 1 Tbs. at a time, scraping down the bowl occasionally. This will take about 5 minutes. Add the potato starch-sugar mixture, then the vanilla and scrape down the bowl. Continue beating until stiff, glossy peaks form, about 1 minute more.
• Pile the meringue in the center of the circle drawn on the parchment, and use an offset spatula or the back of a spoon to spread it into a 9-inch round about 2 inches high around the edge with a slightly concave center about 6 inches wide.
• Put the meringue in the oven, and reduce the heat to 250°F. Bake until crisp, dry, and slightly tan on the outside, rotating the pan about halfway through, about 1-1/2 hours total. (The meringue will puff a little during baking.) Turn the oven off and cool the meringue gradually with the oven door ajar.
• You can make the shell 1 day ahead and leave it in the closed, cooled oven, or store it completely cooled for up to 3 days in an airtight container at room temperature.
• Carefully peel off the parchment and transfer the shell to a serving plate before topping.