Putting ketchup on hot food on Friday night

Hi,

There is a view suggesting that hot solid food, which was heated directly over a flame - like roast heated up in an oven before Shabbos - has the status of a kli rishon even after it is removed from the flame, as long as it retains its heat.

Further, there is a view suggesting that liquids which have already been cooked may not be re-heated on Shabbat, as this would be considered a new act of cooking.

However, one may pour ketchup on solid food which was heated directly over a flame and then removed, on Shabbat. Ketchup is considered a liquid, and we do not combine the two strict views mentioned above, to prohibit this; each view is subject to dispute.

(Rav Moshe Feinstein, Igrot Moshe Orach Chaim 4:74:Bishul 5)

Have a great day,
Mordechai