Approximately three weeks ago, we have explained that it is permissible to warm up a food that was fully-cooked before Shabbat on an electric hotplate on Shabbat as long as the food is dry, such as bourekas, kugels, and the like. Nevertheless, a liquid dish, such as soup and the like, may not be reheated on Shabbat. The reason for this is because of the law that “there is no cooking after cooking,” i.e. once something has been cooked before Shabbat, there is no prohibition to recook it on Shabbat, for this is considered warming, not cooking. However, the prohibition of recooking on Shabbat does apply to liquid dishes even if they were fully-cooked before Shabbat.
Based on the above, we have also discussed that it is permissible to take a food that was fully-cooked before Shabbat and immerse it into another boiling food on Shabbat. It is therefore permissible to place a hard-boiled egg into a pot of boiling water on Shabbat. It is likewise permissible to take a piece of fully-cooked meat and place it into a pot of boiling food on the electric hotplate on Shabbat since “there is no cooking after cooking.”
We must now discuss another aspect of this law. Does the prohibition of cooking on Shabbat apply to something which was already baked? For instance, if a kugel was baked in the oven before Shabbat, may if be reheated in a boiling pot of food on Shabbat?
The above question does not only apply to baked goods and would apply to grilled and roasted items as well. For instance, does the prohibition of “cooking after cooking” to such items, like a grilled steak or roasted nuts,” when reheated on Shabbat on an electric hotplate or not?
Indeed, the great Rishonim disagree regarding this issue. Rabbeinu Eliezer of Metz writes in his Sefer Yere’im (Chapter 102) that although there is no cooking after cooking, there is nevertheless cooking after grilling and baking. He proceeds to bring proofs to his opinion. He adds that for this reason, one must be careful not to immerse baked bread into a hot dish and if one has done so, this constitutes Shabbat desecration.
On the other hand, Ra’avaya (Rabbeinu Eliezer bar Yoel Ha’Levi) rebuffs the Sefer Yere’im’s opinion with a strong proof of his own. Maran Ha’Bet Yosef (Chapter 318) writes that the Ra’avaya’s question on Rabbeinu Eliezer of Metz is a strong one.
In Shulchan Aruch (Chapter 318, Section 5), Maran rules, as follows: “There is someone who says that something which was baked or grilled and later cooked on Shabbat, this constitutes the prohibition of cooking on Shabbat. Others permit this.” The Rama adds: “It is customary to be careful whenever possible not to place bread into a hot dish of food.”
Halachically speaking, Maran Rabbeinu Ovadia Yosef zt”l (in his Responsa Yabia Omer, Volume 8, Chapter 35 and Chazon Ovadia- Shabbat, Volume 4, page 306) rules, as follows: “According to the letter of the law, it is permissible to immerse something which has been baked or grilled into even a boiling dish of food. One who acts stringently and abstains from doing so is especially praiseworthy. Nevertheless, our Ashkenazi brethren customarily rule stringently on this matter, in accordance with the ruling of the Rama.”
Hagaon Harav Shlomo Zalman Auerbach zt”l (in his Shulchan Shlomo, Volume 2, page 320) adds that “Lukshen” or “Yerushalmi” kugel made from noodles that were cooked before the kugel as a whole was baked is considered a cooked food. Thus, even according to the Ashkenazi custom, it will be permissible to place such a kugel into a boiling dish of food on Shabbat. Similarly, croutons which were fried before Shabbat are considered a cooked food, not a baked good, and may be added to a hot soup on Shabbat.
Summary: According to the Sephardic custom, it is permissible to place a food baked before Shabbat into a boiling dish of food on Shabbat according to the letter of the law. However, the Ashkenazi custom is to act stringently in this regard.