filter coffee on shabbat

Question

the subject of making filter coffee on shabbat by pouring hot water from a keli sheni through a filter sitting on top of a cup was raised. i posed this question today to rabbi abadi in har nof. he mentioned the problem of "bishul achar afiyah" and said that it should be avoided. it has been posted here otherwise. can you please clarify? (he said a "french press" would also be a problem of borrer.)