1 scant cup chopped bittersweet or semisweet chocolate, divided
1 cup toasted and skinned hazelnuts, coarsely chopped, divided
3 large egg whites, at room temperature
1/8 teaspoon cream of tartar
2/3 cup sugar
1. Position racks in the center and lower third of the oven, and preheat the oven to 300°F. Line two baking sheets with parchment.
2. Set aside about one-third of the chocolate and nuts for topping the cookies.
3. Combine the egg whites and cream of tartar in a clean, dry bowl. Beat at medium-high speed with an electric mixer until the egg whites are creamy white (instead of translucent) and hold a soft peak when the beaters are lifted. Continue to beat on medium-high speed, adding the sugar a little at a time, taking 1 1/2 to 2 minutes to add it all. The mixture should stand in very stiff peaks when the beaters are lifted.
4. Use a rubber spatula to fold in the chocolate and nuts until just incorporated.
5. Drop heaping teaspoonfuls of meringue 1 1/2" apart on the prepared baking sheets. Top each meringue with some of the reserved chocolate and nuts.
6. Bake for 10 to 15 minutes, until the meringues begin to turn golden.
7. Swap the baking sheets from top to bottom and turn the oven down to 200°F. Bake for another 1 1/2 hours. Turn off the oven and leave the meringues in it to cool completely (another hour). When the cookies are completely cool, serve with a bit of cinnamon grated over them, or store in an airtight container for up to 2 months.
Formulation courtesy of King Arthur Flour