Eruv Tavshilin

Eruv Tavshilin is a ritual that permits cooking and food preparation on the second day of the holiday (Friday) for use on the Sabbath.

Ordinarily on Jewish holidays Jews are permitted to cook and prepare only the foods necessary for that same day. At the same time, Sabbath meals must be prepared before the Sabbath begins as it is not permitted to cook on the Sabbath.
 
So what happens when the second day of a holiday is Friday and Sabbath follows immediately at the holiday’s end?

For such situations, the rabbis instituted a special ceremony called Eruv Tavshilin. One performs Eruv Tavshilin before a holiday so that one can prepare food for the Sabbath on the holiday.

To perform the ritual of Eruv Tavshilin, symbolically single out food for the Sabbath on the eve of the holiday (Wednesday). Set aside a challah (bread) roll and some cooked food (such as a hard boiled egg or a piece of your favourite Gefilte Fish). Then recite the blessing:

בָּרוּךְ אַתָּה ה' אֱלקֵינוּ מֶלֶךְ הָעוֹלָם אֲשֶׁר קִדְּשָׁנו בְּמִצְוֹתָיו וְצִוָּנוּ עַל מִצְוַת עֵרוּב

Baruch Atah Adonai, Eloheinu Melech HaOlam, Asher Kidishanu B`Mitzvotov, Vitzivanu, Al Mitzvat Eruv.

One continues with the following, which must be said in a language one understands:

בַּהֲדֵין עֵרוּבָא
יְהֵא שָׁרֵא לָנָא לַאֲפוּיֵי, וּלְבַשּׁוּלֵי, וּלְאַטְמוּנֵי, וּלְאַדְלוּקֵי שְׁרָגָא, וּלִמֶעְבֵּד כָּל צָרְכָּנָא מִיּוֹמָא טָבָא לְשַׁבְּתָא.

"With this Eruv we are permitted to bake, cook, keep things warm and light fire and do all that is needed from Yom Tov to Shabbos".

The roll and egg/fish should kept in a safe place and may be eaten on the Sabbath. Once done, the eruv covers all household members and guests, permitting them to cook and prepare food on Friday - the 2nd day of the holiday – for the Sabbath.

If they are eaten before Shabbos, a Rabbi should be consulted how to proceed.

Even those who don't have to cook for Shabbos, still need to do Eruv Tavshilin in order to light Shabbos candles (from an existing flame.)