Heating food with sauce on Shabbat
Question
And if so, may an Ashkenazi eat from this fish or meat on Shabbat?
Answer
Shalom u’vracha
One should be stringent and not heat a dish that contains a noticeable amount of sauce [beyond the mere moisture on the food itself]; see the source.
Source
The issue under discussion is whether a food that is mostly dry may be heated on Shabbat, or whether the very fact that it contains a small amount of liquid already makes this forbidden. The well‑known words of Rabbeinu Yerucham, quoted in the Beit Yosef, siman 253 and siman 318, address this, and there are two versions of his text: either “any food that is mostly sauce,” etc., is considered full cooking, or “any food that has sauce in it,” etc., is considered full cooking. This is discussed at length in Minchat Kohen, Shaar 2, chapter 2, s.v. "ha‑tenaï ha‑sheni"; see also Pri Megadim, siman 253, Eshel Avraham, sec. 41; Shulchan Aruch HaRav, siman 318, § 11; Da’at Torah, siman 318, sec. 15; and Kaf HaChaim, siman 318, sec. 62.