1. Preheat oven to 200ºF. Line a baking sheet with parchment.
2. Using an electric mixer on medium speed, beat egg whites, cream of tartar and salt until soft peaks form, about 2 minutes. Gradually beat in sugar until mixture is glossy with stiff peaks, about 3 minutes. Fold in extract.
3. Spoon meringue into a pastry bag fitted with a star tip. Pipe into 1 1/2-inch stars on sheet, 1/2 inch apart.
4. Bake until firm and crisp but not browned, 1 hour 30 minutes to 1 hour 40 minutes. Slide parchment, with meringues, off sheet onto a wire rack. Let cool completely before removing meringues from parchment.
5. Set a small bowl over a pan of simmering water. Place two-thirds of chocolate in bowl and melt, stirring occasionally. Remove bowl; stir in remaining chocolate until melted.
6. Line a baking sheet with parchment. Dip bottom of 1 meringue in chocolate, wipe off excess against side of bowl and transfer to sheet. Let stand until set. Repeat.