Preheat oven to 225°.
Line a large baking sheet with parchment paper; secure with masking tape.
Place egg whites and cream of tartar in a medium bowl; beat with a mixer at medium speed until soft peaks form. Increase speed to high, and gradually add 1/4 cup granulated sugar and then powdered sugar, 1 tablespoon at a time, beating until stiff peaks form. Add the vanilla; beat just until combined.
Place pecans, 2 tablespoons granulated sugar, and chocolate in a food processor; pulse 6 times or until finely ground. Fold chocolate mixture into egg white mixture.
Spoon the batter into a large zip-top plastic bag. Seal bag; carefully snip off 1 bottom corner of bag. Pipe 30 S shapes on prepared baking sheet.
Bake at 225° for 1 1/2 hours. Turn oven off; cool meringues in closed oven 2 hours or until dry. Carefully remove the meringues from paper.