Im making my son's 3rd b-day cake and wanted to try the MMF will I need to put a layer of bc down first? How will does this hold up in the heat? and the will the mmf recipe cover a 11x15?
I can answer your first question. Yes, in my experience you do need to put buttercream down first. The MMF needs something to stick to. Without it the MMF will slide off the cake.
When saying "heat" do you mean having MMF outdoors? If it does anything is will dry out more.