Preheat your oven to 300 F and line a baking sheet with parchment paper.
In a large clean bowl, combine the egg whites and salt. Using an electric mixer, beat on medium-high speed until soft peaks form, about 2 minutes. Gradually add the sugar one tablespoon at a time while continuing to beat.
Continue beating until stiff, glossy peaks form and the meringue holds its shape firmly, about 3 to 4 more minutes.
Sift the cornstarch over the meringue and add the vanilla extract. Gently fold everything together with a spatula using slow, sweeping motions. Be very careful not to deflate the mixture.
Scoop the meringue onto the prepared baking sheet and gently shape it into a thick, domed round about 7 to 8 inches across. Use the spatula to create soft, cloud-like swirls on the surface.
Bake for 22 to 25 minutes, until the outside is lightly golden and set but the inside still feels slightly soft and marshmallow-like. Let it cool on the baking sheet for 5 minutes before serving. Cloud bread is best enjoyed fresh within an hour of baking while it is still light and pillowy.