Learn שולחן ערוך ס’ שי”ח סע’ ז & ח which brings two opinions whether one may place a fully cooked food on top of a pot which is on the fire.
https://hebrewbooks.org/pdfpager.aspx?req=60388&st=&pgnum=277
What is the difference between סע’ ז & סע’ ח
Why does the Shulchan Aruch conclude in סע’ ח that it is permitted but leaves סע’ ז unresolved?
Learn מגן אברהם ס’ שי”ח ס”ק כו
https://hebrewbooks.org/pdfpager.aspx?req=14325&st=&pgnum=155
Review שולחן ערוך ס’ רנ”ג סע’ ה
https://hebrewbooks.org/pdfpager.aspx?req=60388&st=&pgnum=52
And שולחן ערוך ס’ רנ”ג סע’ ג
https://hebrewbooks.org/pdfpager.aspx?req=60388&st=&pgnum=51
Why does the Shulchan Aruch permit one to place a cold pot of food on top of a pot on a fire but in סע’ ג only permits חזרה?
Learn מגן אברהם ס’ רנ”ג ס”ק לג
https://hebrewbooks.org/pdfpager.aspx?req=14325&st=&pgnum=27
Learn דגול מרבבה on the מגן אברהם
Learn פרי מגדים אשל אברהם ס”ק לג
https://hebrewbooks.org/pdfpager.aspx?req=41248&st=&pgnum=163