Yesterday we explained that our Sages forbade leaving a food which is not yet fully-cooked on a stove filled coals, for they were concerned that one would stoke the coals in order to raise the heat and intensity of the fire.
We have mentioned that according to Maran Rabbeinu Ovadia Yosef zt”l, it is permissible, according to the letter of the law, to leave a food which is not yet fully-cooked on a gas stove top common nowadays, for these stovetops do not contain any coals. Although there is some room for stringency here by covering the flame with an aluminum sheet and covering the knobs so that one does not inadvertently raise or lower the flame on Shabbat, nevertheless, it is permissible to leave such foods on an open flame before the onset of Shabbat since the stove does not contain coals.
Based on this, we can infer that an electric hotplate used on Shabbat (“Plata”) whose heat-source within it is completely indiscernible and is covered with a layer of metal from its production retains the same law as a stove with the coals “removed or covered” and one may act leniently and place a pot of food on top of it before the onset of Shabbat in order to continue being cooked on Shabbat. One need not place a metal sheet on top of it since the heat-source within it is already covered by metal. Hagaon Harav Moshe Feinstein zt”l rules likewise.
There are other reasons for leniency discussed at length in the works of the Poskim. There are nevertheless those who customarily act stringently and place a metal sheet on top of the hotplate in order to separate between it and the pot. However, as we have mentioned, the Halacha follows that there is ample room for leniency even without an additional layer of metal.
Among Sephardic and Middle Eastern Jews who follow the rulings of Maran Rabbeinu Ovadia Yosef zt”l, it has already become the prevalent custom to act leniently in this regard and leave the Shabbat Chulent directly on the electric hotplate (without any extra layer of aluminum) before the onset of Shabbat, even if it not yet full-cooked. Among those who act leniently in this regard are many great Torah scholars and righteous people.
There are nevertheless some people who are not fluent in Torah law and wish to keep Shabbat but mistakenly think that it is permissible to cook on top of an electric hotplate on Shabbat. In this way, they cook, fry, and do everything else they would do on a regular weekday, just that this is being done on a hotplate. They should be warned that cooking on an electric hotplate on Shabbat constitutes actual Shabbat desecration. The above leniency refers only to leaving foods which are not yet fully cooked on the electric hotplate before the onset of Shabbat or to place dry foods which were fully-cooked before Shabbat onto the hotplate on Shabbat, as we shall discuss, G-d-willing.
Summary: One may place a pot of food which is not fully-cooked on an electric hotplate before Shabbat and one may do so even without placing a layer of metal on top of the hotplate.
All of this applies to leaving a pot of food on a hotplate before the onset of Shabbat; however, placing the food on Shabbat itself requires that several other conditions be met, as we shall soon discuss, G-d-willing.