1Heat oven to 275ºF. Line cookie sheet with heavy brown paper or aluminum foil.
2Beat egg whites and cream of tartar in medium bowl with electric mixer on high speed until foamy. Beat in sugar, 1 tablespoon at a time; continue beating until stiff and glossy. Do not underbeat. Fold in chocolate.
3Drop meringue by 1/3 cupfuls onto cookie sheet. Shape into about 3-inch circles, building up sides. Bake 1 hour. Turn off oven and leave meringues in oven with door closed 1 1/2 hours. Finish cooling at room temperature.
4Place strawberries in blender or food processor. Cover and blend on medium speed until smooth. Fill each meringue with about 1/2 cup frozen yogurt. Top with strawberries.