Preheat oven to 225F and line baking sheet with silicone baking mat/parchment paper.
In a medium bowl, whisk together the sugar, cornstarch, and salt. Set aside.
Place the egg whites, cream of tartar, and vanilla extract into the bowl of an electric mixer fitted with the whisk attachment. Begin whisking at medium-high speed until the mixture is foamy.
Gradually add the sugar mixture and lemon zest and continue whisking at medium-high speed until stiff peaks have formed. The mixture should also be glossy at this point.
Fill the piping bag with the meringue and pipe onto the baking sheet; pull up on the piping bag to create the tip. Remember: they don't need to be piped too far apart!
Bake for 60-70 minutes. The cookies may feel a little soft in the middle, but they'll firm as up they cool. Turn the oven off and allow the cookies to cool int he oven for about an hour. Remove the cookies from the oven and transfer them to a wire rack; they should take about 10-15 minutes to cool.