I don't know about anyone else but I find cutting mud cake to be a bit hard to cut cleanly and into smaller slices because of the denseness of them.

Today I purchased the lovely Rocky Road Mud Cake from Woolworths (it really is a winner). They arrive in the shop frozen and are then put on display.

I have found the best way to cut them cleanly and into small portions by doing this: Firstly boil your jug, then put into a tallish container...I have a large stainless steel water jug. Pop two largish long handles knives in there and let them get hot.
Take out out and cut your first slice. Then put back into jug (after wiping it down or washing off any cake residue)
Then take the other hot knife and do the same again. You may need to put a small wash cloth or something similar over the blade as you push down on it as it is quite hot...if the cake is still semi frozen as mine was today.

I was able to cut my mud cake into 18 slices as we wanted to only give each person a taste (a retirement village scenario) as it is very rich.

Much easier than trying to do it with a cold knife...well it was for me anyway.