I live in the Bahamas and it's wicked humid here. I use only Indydebi's recipe and I don't have any problems with it, even when the cake is taken from my air conditioned house to outside. I mix all the ingredients together, except the PS, until creamy and smooth (takes just a minute or two) then add 2/3s of the PS and mix again until smooth, then add the rest of the PS and a little more of the milk. I never sift the PS, I just pour it straight from the bag. I will sift if I have to use the PS from a box and it's lumpy, but otherwise I don't.
I often use the icing as soon as I make it, however I try to make it in advance and let it sit for awhile because it's creamier and smoother that way.
"One of the sanest, surest, and most generous joys of life comes from being happy over the good fortune of others."
- Robert A. Heinlein
"One of the sanest, surest, and most generous joys of life comes from being happy over the good fortune of others."
- Robert A. Heinlein