Before spreading the sorbet, let soften at room temperature; or cut the sorbet into chunks, and microwave in six-second intervals (stirring in between) until smooth.
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.
Meanwhile, in a small bowl, stir together remaining 2 tablespoons sugar and the cornstarch; beat into egg-white mixture. Beat in vinegar and vanilla.
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.
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.
Using a flexible spatula, spread and smooth the meringue mixture, creating a well in the center for the filling.