How to make an exploding creeper cake?

My daughter wants to have a Minecraft themed birthday party, so I thought it would be a cute idea to make an exploding creeper cake. I want it to be safe enough to where the cake will explode on all the guests without hurting anybody. There would also be a backup cake to eat, but I think it would be fun for the kids if they could eat the cake that exploded, too. I'd like to light a fuse and two seconds later have it explode. Is this possible?

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