Don’t forget to make an Eruv Tavshilin this year on the eve of the last days of Pesach, Thursday, 5 April. Please print this page out and hang it on your wall or fridge to remind you to perform the Eruv. In order to avoid forgetting one may even make the Eruv on Wednesday night as well.
The prohibition against the performance of labor on the Festivals (Exodus 12:16) specifically excludes preparation of food and that is why we are permitted to cook on Yom Tov. However, it is still forbidden to prepare food on a festival for use on one day for the next or from Yom Tov to a week day. This would mean that when a Festival falls on Friday, it would not be permitted to prepare food on Friday needed for Shabbat.
The Rabbis considered that an undue burden so they permitted one to cook on Friday for Shabbat. Nevertheless, in order to prevent the impression that one may cook on a Festival for the next day, the Rabbis attached a condition to preparation of Shabbat meals on a Festival - i.e; such preparations may not be made unless they were begun before the Festival (Pesachim 46b). In other words, if a Festival falls on Friday, preparations for the Shabbat meal must begin on Thursday (Wednesday, if a festival is on Thursday and Friday). This preparation is effected by the performance of an eruv tavshilin, literally, mingling of cooked foods. The eruv consists of a matzah, along with any other cooked food (such as fish, meat or an egg) that are set aside on the day before the Festival to be eaten on the Shabbat. The eruv foods are held in the hand (Orach Chaim 527:2) and a blessing is recited. Since the person setting the eruv must understand its purpose, the accompanying declaration must be said in a language he understands.
The food is handed to another member of the household other than the person making the eruv who has in mind to acquire the food on behalf of all members of the household and anyone else wishing to rely on the eruv. The one making the eruv recites.....
I hereby grant a share in this Eruv to anyone in this city, who wished to participate in it and to depend upon it.
The one to whom the eruv food was handed raises them a tefach (hands breadth) which is the manner in which the food is acquired for all the participants, and then returns them to the one making the eruv, who recites the following blessing and formula:
ברוך אתה ה' אלקינו מלך העולם אשר קדשנו במצותיווצונו על מצות ערוב
Blessed are You, Lord our G-d, King of the universe, who has sanctified us with His commandments, and commanded us concerning the Mitzvah of the eruv.
Through this it shall be permissible for us to bake, cook, to put away (a dish to preserve its heat), to kindle a light, and to prepare and do on the Festival all that is necessary for the Shabbat - for us and for all Israelites who dwell in this city.