13) When Yom Tov falls on Thursday and Friday (like this year – 5774), and one made his ET on Wednesday, he may not cook for Shabbos on Thursday, only on Friday. There are no exceptions! (Note: For those who followed the technical background behind the ET given in the introduction, bear in mind that for us who keep two days of Yom Tov, the first day is mid’oraisa, while the second day is mid’rabanan. According to the Torah, the second day, Friday, is actually a weekday – or Chol Hamoed. Thus there can be no possible heter/permit mid’oraisa to cook on Thursday for Shabbos, because mid’oraisa one can cook all day Friday which is not Yom Tov! See?) ‘B’di-avad’ (i.e. if the deed was done and the food was cooked on Thursday), the Mishnah Berura rules that the food may be eaten on Shabbos, and there is no penalty.
14) Question: In a year like this one, when we make two ETs back-to-back (Sukkos and Shemini Atzeres), can one make only one ET and have it count for both (assuming he can keep the food fresh and around through both Yomim Tovim)?
Answer: That is a matter of ‘machlokes’/dispute among the authorities. The Shulchan Aruch rules that we should make two separate ETs. ‘B’di-avad’ - in case he made only one (with both Yomim Tovim in mind), and he did not even make a second declaration on the same food before the second Yom Tov (see #12) which would have been second-best - he may rely on the lenient opinion and cook on the second Yom Tov for Shabbos.
15) Important: The ET food must remain intact until the Shabbos preparations are completed. If it got lost or destroyed, one may not make any more preparations! (See #7 about relying on the Rav’s ET in that case.) Remember: If the baked food got lost but the cooked food is still intact, that’s fine (See #2). Even if some of the cooked food got lost, but at least a kezayis remains, that’s also fine (See #3)!
16) Once the Shabbos preparations are complete, the ET foods may be eaten, even while it is still Yom Tov. However, we learned that eating them on Shabbos is preferable so that they may be used again for a mitzvah! (See #4 – Wow, we’re really reviewing our previous lessons today!)
17) If the ET got lost or destroyed in the midst of the Shabbos preparations, one may complete whatever dish he had started - even if he had merely, say, pared vegetables for a stew, kneaded dough for bread etc.
18) This halacha is sharp: Question: Suppose one’s ET food was lost or destroyed on Yom Tov (Friday) before he prepared for Shabbos, but he has Yom Tov food all prepared which he hasn’t eaten yet. Can he put away his Yom Tov food for Shabbos and now cook more for Yom Tov?! (Boy, these Rabbis think of everything!)
Answer: It depends: If that Yom Tov food was cooked before the ET was lost or destroyed, then yes, because he COULD HAVE designated it for Shabbos food at that time! However, if that Yom Tov food was cooked after the ET was lost or destroyed, he may not!
(Note: It goes without saying that if someone cooked Yom Tov food, he may not, on Yom Tov, change his mind and designate it for a weekday, and then go and prepare other food for Yom Tov!)