Beat egg whites and cream of tartar in large bowl with electric mixer on medium speed 5 minutes or until soft peaks form. Gradually add granulated sugar, beating on high speed until well blended. Add powdered sugar, 1 Tbsp. at a time, beating well after each addition. (Meringue will begin to turn glossy.) Continue beating until stiff peaks form. Stir in cranberries and chocolate. Spread onto prepared baking sheet to within 1/2 inch of edges of baking sheet.