1. Preheat oven to 300°. Line a sheet pan with parchment paper, trace a 9-inch circle in the center, and turn the paper over.

2. In the clean bowl of a standing mixer with a whisk attachment, beat egg whites until frothy.

3. Add salt and continue beating. As soft peaks form, slowly add sugar in a thin stream, beating as you go.

4. Once sugar is incorporated, beat on high speed until firm, shiny peaks begin to form, about 2 more minutes.

5. Stop beating; then gently fold in vanilla, vinegar, and cornstarch with a spatula.

6. Spoon the meringue into the center of the traced circle and spread it out to the edges, creating a shallow well in the middle.

7. Put into the oven, reduce heat to 250°, and bake 1-1/2 hours.

8. Turn off the oven, leaving meringue inside until it turns crisp and pale, but still a bit soft inside, about 1 hour.

9. Remove from oven and let cool completely.