Q. See question above. Can one use solid cream cheese for a coffee that will melt, when placed in Keli Shelishi?
A. As far as the Bishul prohibition is concerned regarding congealed fat, butter or margarine, Poskim disagree if they are considered a ‘Davar Yovesh’ (dry food) or not since when heated they will melt. Mishna Berura (318: 16) and other Poskim are lenient.
In our case, since as is we deal with a Keli Shlishi or coffee that has been poured in a third vessel, where Bishul does not usually apply according to most Poskim, it would be permitted. This can also be compared to placing an ice cube
in a drink, where it will melt.
Rabbi A. Bartfeld as revised by Horav Dovid Pam, Horav Aharon Miller and Horav Chanoch Ehrentreu Shlit’a.