Here is a simple recipe that I use, and it works well for me. Just make sure that it is not too warm, as it gets runny (i.e. if you microwave it after it was refridgerated). This is a big batch, so may just do a half.
3 c powdered sugar
1.5 lb. cream cheese (room temp.)
3/4 lb. salted butter (room temp.) (or if using unsalted, add a little salt).
Mix everything together in an electric mixer with the blade attachment (not whisk). Start carefully, so that the powdered sugar does not “explode”, then gradually move unto full speed. Scrape the sides a couple of times to make sure everything is incorporated. Mix until the mixture is white and smooth ( as compared to yellowish and having small lumps).
Yes, I would refridgerate them.