Ive tried so many but the only one Ive is the wilton I tried to use butter on some of them and when I woke up the next morning, to my horror I found the buttercream had melted all the way down making the fondant look "pregnant"...Most buttercream recipes use butter is there any other you guys love to use and is a no fail with fondant? Please let me know.

use all shortening in place of the butter. Make sure you add extra butter flavor.

i dont use butter in my buttercream i use shortening, and then add butter flavoring, along with almond and vanilla. But my recipe is pretty much the "Wilton class" buttercream recipe and i've never had a problem with putting fondant over it. Make sure its really smoothed out

I use a simple buttercream underneath and after covering a cake with fondant I return it back to the fridge. Or do you leave your cakes outside the fridge?