Step 1: Preheat your oven to 300°F (150°C) and line a large baking sheet with parchment paper.
Step 2: In a perfectly clean glass or metal bowl, beat the egg whites and cream of tartar on medium speed until soft peaks form.
Step 3: Gradually add the superfine sugar one tablespoon at a time, continuing to beat on high speed until the mixture is thick, glossy, and holds stiff peaks.
Step 4: Sift the cornstarch over the meringue and gently fold it in along with the vanilla extract using a rubber spatula.
Step 5: Mound the mixture onto the prepared baking sheet, shaping it into a tall circle with a slight indentation in the center.
Step 6: Lower the oven temperature to 250°F (120°C) and bake for 60 to 75 minutes until the exterior is crisp but still white.
Step 7: Turn off the oven and leave the cake inside with the door slightly ajar for at least an hour to cool completely and prevent cracking.