From: Rabbi Moshe Sofer
To: Rabbi Zalman
The community of Hamburg prepares coffee on Shabbos by pouring boiling water from a kli rishon onto grounds that had been pre-soaked before Shabbos. The Chasam Sofer rules that for completely dry grounds, one cannot protest those who permit this through a non-Jew, but if the grounds retain cold moisture, it is prohibited since most poskim hold there is bishul achar bishul for cooled liquids.
Source: Shu"t Chasam Sofer OC §74