I just made my first cake from scratch ever and jumped into a 3 tier cake with fondant for my daughter's first birthday  I was thrilled everything went as well as it did BUT I had one problem I am looking to solve for the future  I found the most delicious recipe for white cake and used a flour  buttercream frosting that was made by first cooking a pudding made with milk, sugar and flour, letting that cool and them mixing it with butter. It was amazing! I coated the cake with a crumb coat, refrigerated, coated another coat, refrigerated then covered with fondant and decorated followed by refrigerating again. At 10 am I pulled the cake from the refrigerator and let it come to room temp and dry off from condensation for the party at 3. It never really did dry off in that time and become un sticky. Then by 4 the icing had warmed and began to slide down the cake pulling the fondant down and it started to crack. We ate it and all was fine but for the future I can't have this happen again. Im not sure if I just can't use that frosting as a base anymore because it is so light and fluffy (almost like whip cream) when it warms or if it had something to do with refrigerating or what  any suggestions? Also I would love a great buttercream recipe to use under fondant that isn't super sweet but will hold up. Thanks everyone! Oh and here isy first ever cake!

That kind of icing isn't meant to be used under fondant. If you want something less sweet try a meringue buttercream. Swss meringue and Italian meringue would both work.

I've used that frosting before under fondant at least once but didn't have that issue.  Was the room too warm perhaps?  Normally I use either ganache or SMBC under fondant.  The SMBC recipe that I usually use is this one https://fromscratchsf.wordpress.com/2011/03/08/tutorial-swiss-meringue-buttercream/.  This uses less sugar than most other recipes which is perfect for my family since we don't like super sweet frosting.  If you decided to try it, make sure you use unsalted butter.  It makes a big difference.