1Cut 1 inch off top of store bought or prepared baked cake. Hollow out remaining cake, leaving a 1/2 inch shell. Dissolve 1/2 package of the jello in water then refrigerate. When jell-O begins to set up, beat until fluffy. Fold in Cool Whip until blended.
In another bowl, combine fruit, macaroons, marshmallows and pieces of cake that were removed. Combine both mixtures and place in the hollowed out cake. Replace top of cake and frost with fluffy frosting.
Place butter in mixing bowl and beat on medium speed until creamy. Add evaporated milk, and 1 cup of the powdered sugar and Jell-O powder mix; mix for 1 minute on low then on medium about 2 minutes. Add remaining powdered sugar, 1 cup at a time, until all sugar is incorporated- if it's too thick to spread, add a little more milk one teaspoon at a time, and beat until smooth. If too thin add a little more powdered sugar.