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An Eruv Tavshilin is a halachic device which allows one to cook food on the Festival for use on the Shabbat that immediately follows.
To allow one to cook on the Festival for use on Shabbat, one must prepare an eruv tavshilin which serves as a reminder that the cooking done on the Festival is for Shabbat only.
This eruv consists of a matzah and something cooked, for example, a boiled egg or a piece of fish, and is prepared before the onset of the Festival.
It symbolically serves as the beginning of the preparation of food for Shabbat. Thus, any subsequent cooking done on the Festival is considered to be a continuation of the preparation begun before the Festival.
If the last day of the Festival falls on a Shabbat, one must prepare an eruv tavshilin on Thursday afternoon before the festival begins so that one can cook on the Festival for Shabbat.
How to make an Eruv Tavshilin
Take a plate with one whole matzah and either a piece of cooked fish, cooked meat or a hard-boiled egg on it, (it is a good idea to wrap the matzah/challah and fish, meat or egg in aluminum foil to easily keep them apart from the rest of the foods in your home). Recite the following blessing:
BA-RUCH A-TAH ADO-NAI E-LO-HE-NU ME-LECH HA-OLAM ASHER KID-E-SHA-NU BE-MITZ-VO-TAV VETZI-VA-NU AL MITZVAT ERUV.
Then recite: “By virtue of this Eruv, we (the members of this household), shall be permitted to cook, bake, keep food warm, carry, light candles and do all preparations on Yom Tov for Shabbat.”
Put the foods you used for the Eruv away, and eat them on Shabbat. NOTE: The Eruv Tavshilin allows you to cook on Friday only for Shabbat, it does not allow you to cook from one day of the holiday to the next (ie: Thursday for Friday). It is permissible to cook only from a pre-existent flame, one that was lit before the onset of the Holiday on Thursday before sunset.
Even if you do not intend to cook food for Shabbos during Yom Tov, you must nevertheless prepare an eiruv tavshilin on Erev Yom tov and recite the appropriate blessing over it in order to be permitted to light Shabbos candles while it is still Yom Tov.
If you are being hosted as a guest during Yom Tov, ask a Rav regarding the permissibility of relying on your host’s eiruv tavshilin.
It’s not just if the second day falls on Shabbos that an eruv tavshilin needs to be made. It’s if either day of Yom Tov falls on Friday.
An important part of Halacha was not mentioned in the above instructions. The one saying the brocho says first “ I hereby grant a share in the Eruv to anyone who wishes to participate in it and to depend upon it ( printed in the siddur). Then the set aside food for the Eruv should be given to one person in the household, or spouse, and they lift it up a tefach, (Approximate 3inches) then they hand it back to the one about to say the brocho who will be cooking or preparing the food for Shabbos, and while holding… Read more »