1. Preheat oven to 225 degrees. Line a baking sheet with parchment paper. With an electric mixer, beat egg whites, cream of tartar, and salt in a large bowl until soft peaks form. With mixer running, add 3/4 cup sugar, 1 tablespoon at a time, beating until stiff peaks form.

2. Meanwhile, in a small bowl, stir together remaining 2 tablespoons sugar and the cornstarch; beat into egg-white mixture. Beat in vinegar and vanilla.

3. Drop dollops of mixture in a line down center of prepared baking sheet. With a flexible spatula or a wet spoon, spread into a 6-by-14-inch rectangle. Make a 1-inch-deep well down the center, leaving a 1-inch-thick border around edges.

4. Bake 2 hours; turn off oven, and let stand (in oven) for 2 hours or up to overnight. Fill with sorbet; top with peaches or almonds, if desired. Cut into pieces with a serrated knife.