Originally Posted by JoAnnB
If you are in a big hurry, and you don't want to risk the microwave, use a grater. The shredded butter warms up in a very short time.
I buy butter in large quantities and keep it in the freezer. If I need it in a hurry, I put it in a zip lock bag and immerse it in cool water. It thaws more quickly.
Dairy and eggs are considered "perishable" and should be kept chilled as much as possible. Selling product to the public requires extra caution that we wouldn't worry about for home use.
That is true JoAnn and in some areas you must refrigerate any butter based icing if you run a licensed commercial bakeries but that also has to do with the kitchen temperature. You would have to follow whatever food safety regulations apply in your area.
Salted butter is considered to be safe for 2-3 days according to Government Dairy Institutes, also the salt and the sugar work to preserve cream and milk when they are not the main content of an icing such as in the Wilton recipe. Wilton itself also recommends that these icings are safe at room temperature below 75F for 2-3 days, I find even longer for home use.
I have been using this same recipe for more than 30 years with absolutely no issues, following the Wilton guidelines.