Well, from the looks of it, they did single layer cakes, each one an inch smaller than the next and stacking it for the icing swirl. The base could be two bundt cakes stacked and using the indents as a guide for the carving.
If not bundt cakes, just stack 4 layers of cake and make the indents carvings to look like the crimped edge of a cupcake liner. You could use a corer tool to slide down the side, etc......
HTH - they do have a huge pan by Wilton, I think it's $29.99 but they have a half-off coupon going right now. I have been tempeted to get it but money is tight and my storage space is even worse so I think I may try to do it myself. Good luck with it and have fun - really cute design you chose.
do you have a sports ball pan? you can carve out of 3-4 6in layers and half of a sports ball
I dont have a sports ball pan...
or you could stack lots of rounds, then carve. put on a very thick layer of buttercream and cover with fondant. then take something- don't know what, maybe a thick dowel- and make indents in the buttercream. does that make sense?
depending on how many layers you do, you'll have to dowel the cake like its 2 tiers.