1Heat oven to 325°F. Generously grease and lightly flour bottom and side of 9-inch springform pan.
2Make cake batter as directed on box; set aside. In medium bowl, beat 3 egg whites with electric mixer on high speed until soft peaks form. Beat in sugar, 1 tablespoon at a time; continue beating until stiff and glossy.
3Spread two-thirds of the meringue up side of pan (do not spread on bottom of pan). Pour cake batter into pan; top with remaining meringue. Cut through meringue on top of cake and cake batter with tip of knife to swirl meringue through batter.
4Bake about 1 hour 30 minutes or until toothpick inserted in center comes out clean. Cool 10 minutes. Run knife around side of pan to loosen cake; remove side of pan. Cool completely, about 1 hour. Store loosely covered.