Preheat the oven to 325°F. Line a large baking sheet with parchment paper.

In the bowl of an electric mixer, place the egg whites. Using medium speed, beat until the whites are frothy. Add the cream of tartar and beat on medium-high until soft peaks form, about 2 minutes. Gradually add the sugar 1 tablespoon at a time, beating constantly and taking about 2 minutes. Add the vanilla and salt. Beat until very stiff and glossy and the meringue holds a peak when the beater is lifted straight up, about 2 minutes longer. Using a rubber spatula, gently fold in the hazelnuts and ginger, and then the melted chocolate (leave some white streaks for a marbled appearance).

Dab a bit of the batter on the backside of the parchment at the corners to secure the parchment to the baking sheet. Immediately drop the batter by heaping tablespoons onto the baking sheets, spacing 1 inch apart.

Bake cookies until dry and crisp on the outside but still soft inside, about 10 minutes. Place the pan on a wire rack and cool the cookies 10 minutes. Gently transfer the cookies to wire racks and cool completely. Store the cookies in an airtight container up to 5 days.