All of the components (crumble, cake, apples, etc.) need to be cold when assembling the cake. If the ice cream begins to melt at any point during assembly, put the whole cake in the freezer for 20 minutes for it to firm up again.
Remove the cake from the fridge and use a serrated knife or cake leveler to carefully level off the cake if it formed a dome top. Then, using a serrated knife or cake leveler, carefully cut the cake in half so you now have two cake layers. Place the cake in the freezer for 10 minutes to firm up.
To assemble, place one cake layer on a sturdy surface (a plate, a cake stand, etc.), although make sure it can fit in the freezer.
Pipe a ring of whipped cream on top of the first cake layer. Spoon half of the cold apples into the center, then sprinkle some of the crumble on top of the apples.
Place the second cake layer on top, pipe a ring of whipped cream, and spoon the second half of the cold apples into the center. Sprinkle a little more of the crumble on top of the apples. Place the cake in the freezer for 20 minutes.
After the 20 minutes, remove the cake and ice cream from the freezer and discard the plastic wrap from the ice cream. Place the whole ice cream layer on top of the apples.
Frost a thin layer (crumb coat) of whipped cream on the tops and sides of the cake. Place in the freezer for 30 minutes. This will make it easier to fully frost the cake.
After the 30 minutes, finish frosting the cake with the rest of the whipped cream.
Sprinkle the remaining crumble on top of the cake. Let the cake set in the freezer for one hour. Store the cake in the freezer until ready to slice and serve. Enjoy!