These light-as-air treats, flavored with vanilla, are by One Girl Cookies.
Preheat oven to 200 degrees. Line baking sheets with parchment paper.
In the bowl of an electric mixer fitted with the whip attachment, beat egg whites for 2 minutes on medium speed. Add vanilla, salt, and cream of tartar. Increase mixer speed to high and beat for 30 seconds. Begin adding sugar, about 1 tablespoon at a time; continue to beat, with mixer on high speed, until stiff peaks form, about 2 more minutes.
Transfer meringue to a large pastry bag fitted with a star tip (Ateco #69 or #849). Pipe 2 1/2-inch circles onto prepared baking sheets, spacing cookies an inch apart.
Bake until meringue is crisp and dry, 1 1/2 to 2 hours. Transfer to a wire rack to cool. Meringues will keep in an airtight container at room temperature for 3 to 4 days.