I’m baking my wedding cake and I’m very good with fondant and decorating but when it comes to the cake I have a problem! When I cut into it the cake crumbles and falls apart! I’m trying a new recipe for marshmellow fondant and am going to see if it cuts easier and helps with the crumbling.

Also I’ve been using box cake mix if that matters. This afternoon my friend and I are getting together to make a practice cake!

Please any advice on making my cake stick together when I cut it? Thanks!
No I was using butter. It’s what it called for. So I can substitute oil? Which kind?
My mom said she does a jar of water in the oven too. And she freezes the cake over night. I know it’s easier to ice if u do that but does that help with the crumbling?