Making the cardboard stand: Cut out a circle from thick paper the same size as the cake pan, cover it with aluminum foil, and then you can get to work! You will be able to move the cake smoothly.
Making the chiffon cake container: Stick a knife into the cake about 1.5~2 cm from the edge, and cut out the insides. Slice the removed portion, and place underneath the other piece.
Making the tiramisu cream: add the mascarpone to a bowl, mix well with whipped cream, and then add in granulated sugar, egg yolks, and rum in that order.
Whip the cream in a separate bowl until soft peaks form, add to the bowl from step 2,and thoroughly mix with a rubber spatula.
Pour the cream, blueberry jam, cream, mango jam, cream, and strawberry jam into the chiffon cake in that order. (Cut the top part of the chiffon cake depending on the amount of jam used.) Stabilize the perimeter of the cake using plastic cake film. Wrap the cake in plastic wrap and let sit in the fridge overnight.
Decorate with your favorite fruit, make a glaze with nappage, and it is done.
It may look like a cake, but it is tiramisu! Refrigerate until you are ready to eat it.
Tip: I tried cutting it after leaving it in the fridge for just a short amount of time, but it is basically tiramisu! It is pretty difficult to cut it cleanly.