Preheat oven to 200°. Line several rimmed baking sheets with parchment paper.
In a large bowl, beat together egg whites and cream of tartar with a mixer at high speed until soft peaks form. Add granulated sugar, confectioners’ sugar, vanilla, and salt, beating until incorporated. Continue to beat at high speed until stiff peaks form, approximately 3 minutes. (Meringue will look glossy.) With mixer on low speed, add hazelnuts, beating until incorporated.
Transfer mixture to a piping bag fitted with a very large open-star tip (Ateco #848). Pipe 72 drops onto prepared baking sheets.
Bake for 1 hour.
Turn oven off, and let meringues remain in oven with door closed overnight. (This will help meringues dry out and form a crispy shell.)
Dip bottom of meringues into melted chocolate, letting excess drip off. While chocolate is still warm, dip bottoms of meringues in additional hazelnuts, if desired. Place meringues onto sheets of wax paper. Let chocolate harden.
Store meringues at room temperature in an airtight container with layers separated by wax paper until ready to serve, up to 2 days.
Recipe by TeaTime Magazine at https://teatimemagazine.com/chocolate-hazelnut-drops/