Timer for cooking on Shabbat and Blech

1.May one cook on shabbat by placing a crock pot or burner on a timer and placing raw food into it and then the timer will turn on the crock pot/burner and will cook it ON shabbat ? May one reheat food this way ? Even food with liquids ? 2. I read that one may not do chazara on shabbat even with totally cooked dry food by placing on a blech directly over the flame -why not ? how can this be michzeh kemevashel since no one cooks with a blech during the week ? Thank you

According to the Spharadi Minhag it is forbidden to place even fully cooked food in a crock pot before Shabbat to keep it warm on Shabbat, and therefore any placement of even fully cooked food in it on Shabbat is also forbidden, kal vehomer. The reason is that use of a crock pot is considered a hatmana. Among the Askenazic poskim there is a disagreement. HaGaon Rav Shlomo Zalman Orbach ZT”L forbids the use of a crock pot on Shabbat for the same reason of hatmana. HaGaon Rav S. H. Wozner, Sh’lita, differs and holds that a crock pot is not hatmana, and using it is only a question of cooking; therefore, one may place food that has started to cook in the crock pot before Shabbat as long as it is turned on before Shabbat. Rav Wozner, Sh’lita forbids placement of food with liquid in the crock pot on Shabbat because it is considered cooking; placement of fully cooked dry food in the crock pot on Shabbat is forbidden because of “mihzeh kemvashel,” even though the purpose is only to reheat, not to cook. According to all opinions, it is forbidden to cook food by having a timer turn on the crock pot on Shabbat. It makes no difference whether the uncooked food is placed in the crock pot before Shabbat or on Shabbat. Any use of a burner, an open flame or other uncovered source of heat, e.g. an electric burner is forbidden according to all opinions, even for keeping food warm that had been fully cooked before Shabbat. (Mishna B’rura Siman 253, Sa‘if 100, Sh’mirat Shabbat Kehilchata Perek 1, Sa‘if 26.) Cooked food placed on a blech may be removed and returned under the following conditions: 1) there is the intent to return, 2) the vessel is constantly held, 3) the food is completely cooked, 4) the food is still slightly warm. The food may be moved to a covered flame that is even hotter, as long as this is not a new hatmana. See Mishna B’rura Siman 253, Sa‘if 2. Birkat HaTorah v’HaAretz HaRav Yehuda HaLevi Amichai http://www.toraland.org.il