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Preheat the oven to 350°F /180°C and place the oven rack in the middle position.
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Draw a 9 inch (23 cm) circle in the middle of a piece of parchment paper large enough to cover a large rimmed baking sheet. Turn the paper over, and place the parchment paper on your baking sheet. The drawn side is facing down. Set aside.
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Wipe your mixing bowl and beaters with some distilled vinegar then wipe dry with a lint free cloth.
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Add the egg whites with a small pinch of Kosher salt to a bowl of a stand mixer fitted with a whisk attachment. Turn the speed to medium-high and whisk until the egg whites become foamy and hold soft peaks.
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With the motor running add the sugar one tablespoon at a time, whisking between each addition. This will take some time, about 5 minutes, but it prevents the egg whites from deflating. When all the sugar is added, turn the speed up to high and beat until the egg whites are glossy and hold stiff peaks and all the sugar is dissolved, about 2-3 minutes. Test if the sugar is dissolved by rubbing a small piece of whipped egg whites between your fingers. If it feels course, then the sugar has not fully dissolved. If so, continue beating the egg whites or a minute more, but be careful to not over beat the meringue because it will deflate.
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Remove the bowl from the mixer and sift the cornstarch over the meringue. Add the lemon zest and vinegar then carefully fold the ingredients into the meringue until evenly combined.
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Pour the meringue on to the parchment paper aiming for the middle of your circle. Spread out the meringue to evenly fill the circle.
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Place in the oven and turn the heat down to 300°F / 150°C Bake for 1 hour then turn off the oven. Keep the oven door closed no peeking. Cool the meringue in the oven for an hour, or until it reaches room temperature.
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You can make the meringue a day ahead and store in an airtight container on the counter. A cool oven is a great place to store the meringue overnight. Do not refrigerate.