For my sugar cookies I use a powder sugar icing. (P/S, butter, milk, vanilla, and coloring) I use this because I prefer the taste to RI. After it sits awhile you can see white specks in it. Any ideas of what I am doing wrong?
Are you sifting your sugar? The only things I can think of is small lumps of sugar or butter, which was not completely incorporated into the mixture.
you don't list it with your ingredients but salt will do that --
I always used cane powdered sugar other sugars were not reliable --
It might also be the cornstarch in your powder sugar