Thanks so much for sharing your experience costumeczar, I will try and cook the sugar to 255 egrees and use a part of shortening.
Glad to know it stands up ok in an air conditioning room. What percentage of confectioner´s sugar do you mean and do you add it before you cook the sugar/syrup or after when you are whipping?
I've seen different amounts...You add it to the icing after you've made it, just add a cup of confectioner's sugar to one batch of buttercream, maybe? You don't need to be quite as precise with buttercreams as you do with cakes, so you can experiment to see what gets you a texture and flavor that you like. I've mixed half IMBC and half confectioner's sugar buttercream before to get a hybrid.