The frosted cake can be stored in the refrigerator, covered, up to two days. Let stand at room temperature for an hour and garnish with the pineapple rounds before serving.
As Martha demonstrated on Martha Bakes, instead of trimming the cakes, you can place a cardboard round on a cake plate or cake stand and top with the first cake layer. Tuck parchment paper strips under round to cover perimeter of cake plate. Proceed with frosting, then remove parchment strips.