Let egg whites stand in large bowl at room temperature 30 minutes. Preheat oven to 300 degrees F. Line cookie sheet with parchment paper or lightly greased foil.
Beat egg whites and cream of tartar on medium to high speed until soft peaks form (tips curl). Gradually add sugar, about 1 tablespoon at a time, beating until glossy and stiff peaks form (tips stand straight). Fold in 1/4 cup of the chocolate and 1/4 cup of the nuts.
Drop meringue in six mounds 2 inches apart on prepared sheet. Using back of spoon, swirl the top of each meringue into a high tip that curls.
Place meringues in oven; immediately decrease oven temperature to 200 degrees F. Bake 1-1/2 hours or until crisp and dry on outsides. Cool completely on sheet on wire rack. Gently peel cooled meringues off parchment or foil. To serve, sprinkle with remaining chocolate and nuts.
Store meringues in an airtight container at room temperature for up to 24 hours. Makes 6 meringues.