Guava Cake

1.Prepare cake batter according to package directions replacing the water called for on the box with guava juice. (some call for 3 eggs and 1/3 cup oil and 1 cup water but if the directions are different follow the box directions). Bake cake in a greased 9X13 pan according to package directions. Let cake cool completely.
2.While cake is baking prepare the cream cheese layer and guava topping.
3.For the cream cheese layer: In a medium mixing bowl, beat cream cheese with hand mixer until fluffy. Add 1/3 cup sugar and vanilla and beat in. Slowly fold in the Cool Whip and refrigerate until ready to use.
4.For the Guava Topping: In a medium sauce pan, bring the 2 cups guava juice and 1/2 sugar to a boil. Make a paste out of the cornstarch with about 2-3 tablespoons of water. Remove guava juice from heat and stir in the cornstarch mixture until combined well. Return mixture to heat and bring back to a boil and boil for one minute stirring constantly. Cool in refrigerator.
5.To assemble cooled cake: Thickly ice the cake with all of the cream cheese mixture. Glaze the top of the cake with guava topping. Refrigerate until ready to serve.