Hi. I'm a super newbie and am going to attempt making a monster truck cake for my son's birthday. I've looked through several buttercream icings (chocolate specifically) for using under fondant and have a question.
Some of the recipes say the icing crusts...do I want this for under fondant or doesn't it make a difference?
Thanks!

I use a crusting buttercream under my fondant. 1/2 butter 1/2 shortening.

You definitely want the icing to crust so that the fondant goes on smooth and holds it's shape. If the icing underneath is soft, the fondant will have lumps and maybe even sagging.

You do NOT have to use a crusting buttercream under the fondant. I use IMBC and it does not crust. If you are using a non-crusting icing, simply refrigerate the cake prior to applying the fondant to resolidify the butterfat in the icing and the fondant will go on nice and smooth.