Grease and flour round cake pans. Bake cake according to package directions, substituting guava juice for the water. In a medium mixing bowl, beat cream cheese with hand mixer until fluffy. Add sugar and vanilla and beat inches Slowly fold in the Cool Whip and refrigerate until ready to use. In a medium sauce pan, bring the 2 cups guava juice and sugar to a boil.
Make a paste out of the cornstarch and a small amount of water. Remove guava juice from heat and stir in the cornstarch mixture. Return to heat and bring back to a boil and boil for one minute. Cool in refrigerator.
To assemble cooled cake:.
Thickly ice the cake with all of the cream cheese mixture. Glaze the top of the cake with guava gel. Refrigerate until ready to serve.