The Shulhan Aruch, in a famous ruling, distinguishes between solid and liquid foods with regard to the permissibility of reheating on Shabbat. When it comes to liquids, the Shulhan Aruch rules that "Yesh Bishul Ahar Bishul," which means that once a liquid food has cooled, reheating it constitutes cooking and is forbidden. It is therefore forbidden to reheat cold liquid food on Shabbat in any manner. With respect to solids, however, the Shulhan Aruch maintains that "En Bishul Ahar Bishul," meaning, the food cannot be "cooked" twice. Even after the cooked food has cooled, reheating it does not constitute a new "cooking." It is therefore permissible to reheat solid foods on Shabbat over a covered flame or hotplate. Common examples of such food include rice and kibbeh.
The authorities debate the question of whether or not one may reheat on Shabbat food that is mainly solid, but has some liquid, as well. It must be clarified that we do not refer here to foods that contain liquid inside; nearly all foods have some water inside them. We refer here to a situation such as a roast, or yebra (stuffed grape leaves), which is a solid food but has some gravy sitting on the bottom of the pot. This question depends on how one interprets a certain passage in the Bet Yosef, as well as the correct text of the passage in question. In short, the Minhat Kohen, based on his interpretation of the Bet Yosef, held that a food which is primarily solid has the status of a solid food with respect to this Halacha. Even though it contains some liquid, the food’s status is determined by the majority, and therefore it may be reheated on Shabbat despite the presence of some liquid. It is recorded that the practice in Jerusalem was to follow this ruling.
Hacham Ovadia Yosef, in his work Yehave Da’at, accepts this lenient position of the Minhat Kohen and allows reheating on Shabbat food that contains some liquid. Interestingly, in a recorded public lecture, Hacham Ovadia appeared to express some ambivalence on the matter, and many understood that he rescinded the ruling issued in Yehave Da’at. But in a later publication (Yabia Omer, vol. 9), Hacham Ovadia clarified that he did not retract his ruling, and that he indeed permits warming such foods on Shabbat. He does, however, add that those who are stringent are "worthy of blessing," as they satisfy all opinions. This point is made by Hacham Ovadia’s son, Hacham Yishak Yosef, in Yalkut Yosef. Strictly speaking, though, according to Hacham Ovadia, Halacha follows the lenient view of the Minhat Kohen.
Other authorities, however, disagreed. Hacham Ben Sion Abba Shaul (Israel, 1923-1998), for example, ruled stringently on this issue and maintained that one may not reheat liquid under any circumstances, even if the liquid constitutes the minority of a food which is mainly solid.
As for the final Halacha, those who have a non-Jewish housekeeper working on Shabbat should preferably ask the housekeeper to place such a food on the Blech or hotplate, rather than doing so themselves. This is permissible according to all views. Those who do not have a non-Jew working in their homes may reheat food that contains some liquid, though it is preferable to be stringent in this regard.
Summary: One may reheat on Shabbat (on a Blech or hotplate) dry cooked food that contains some liquid, such as a roast or yebra that has some gravy or juice on the bottom. In order to satisfy all opinions, however, it is preferable to have a non-Jew reheat this food and not to do so oneself.
