Heat the oven to 235°F. Line 2 large baking sheets with parchment paper.
To the bowl of an electric stand-mixer fitted with the whisk attachment, add the egg whites, 2 tablespoons sugar, and the salt. Whisk on low until the mixture begins to foam. Increase speed to high and whisk until smooth, soft, glossy peaks begin to form. Gradually sift in the remaining sugar, continuing to whisk until stiff peaks form. Add the confectioner’s sugar and cornstarch and whisk briefly until incorporated.
Spoon the meringue into a piping bag fitted with a ¾-inch tip (or use a plastic bag with a cut corner). Pipe 4 3- to 4-inch “flowers” onto each baking sheet: Start with a walnut-sized central blob, then surround it with 6 additional smaller blobs to form a flower shape. Be sure to space the flowers well apart on the sheets. Use a knife to flatten each central blob to create a shallow well to serve as a base for the filling.
Place baking sheets gently in the oven and bake 90 minutes or until flowers are crisp to the touch. Let cool on baking sheets for 10 minutes, then transfer carefully to a wire rack to cool completely.