Line two ungreased 18x13-in. baking pans with parchment paper. Place egg whites in a large bowl; let stand at room temperature 30 minutes. Sift confectioners' sugar and flour together three times; set aside.
Preheat oven to 350°. Add cream of tartar, vanilla and salt to egg whites; beat on medium speed until soft peaks form. Gradually add sugar, 1 tablespoon at a time, beating on high until stiff peaks form. Gradually fold in flour mixture, about 1/4 cup at a time.
Gently spoon into prepared pans. Cut through batter with a knife to remove air pockets. Bake 25-35 minutes or until golden brown on top. Cool completely, about 1 hour.
Cut with a 4-in. ghost-shaped cookie cutter. Spread half of the cakes with preserves; top with remaining cakes. Place on wire racks over waxed paper.
Transfer frosting to a microwave-safe bowl. Microwave on high 20-30 seconds or until melted; stir until smooth. Spoon over cakes. Add chocolate chips for eyes and M&M's for mouths. Let stand until set.