Make up the cake mix according to manufacturer’s instructions. Use a half sheet tray extender on a lined half sheet tray. Spray the pan and deposit 6 pounds of batter into prepared pan. Bake at 350F until cake springs back lightly when touched. Let cool completely.
Trim the belly and place on a cake board, trimmed side down. Reserve the belly for cake pops. Smooth ice the top of the cake with white buttercreme.
Mix 1tsp citric acid with 2qts cold water. Thinly slice the fruit, soak in prepared water for a few minutes, and place on cake right before serving.
Citric acid helps prevend browning or oxidation in fruit. If you cannot find citric acid, you can substitute fresh lemon juice instead. 1tsp citric acid is about the same as ¾c fresh lemon juice.