1.Bi’ur Ĥametz and Shabbat Meals
When the fourteenth of Nisan coincides with Shabbat, bedikat ĥametz is performed with a berakha on the night of the thirteenth, Thursday night, because it is impossible to seek and eliminate ĥametz on Shabbat. After the search, the ĥametz is nullified like in any other year, and on the following day, Friday, it is burned. It is best to burn it by the sixth seasonal hour of the day, like in any other year (SA 444:1-2). Ĥametz that will be eaten during the first two Shabbat meals is carefully set aside.
If it were permissible, we would certainly eat matza with the Shabbat meals in order to avoid the problem of ĥametz. However, it is forbidden to eat matza on Erev Pesaĥ so that it is appetizing to us at the Seder (see above 13:6). Therefore, we must save ĥametz for the first two Shabbat meals. In order to avoid problems with ĥametz foods, many people cook kosher-for-Pesaĥ foods for that Shabbat. They make kiddush and eat bread with spreads or salads in a room where people will not eat during Pesaĥ. After eating bread, they clean their hands and brush off their clothes, then eat the rest of the meal in the kosher-for-Pesaĥ dining room.
The second Shabbat meal must be completed by the end of the fourth seasonal hour of the day, at which time ĥametz becomes forbidden. Shabbat morning prayers must begin and end early so that the meal can be completed in time (see above 3:6).
After the morning meal, all remaining ĥametz must be gathered from the plates and tablecloth. Since it may not be burned on Shabbat, it is a good idea to flush it down the toilet and thus completely destroy it. People generally plan their Shabbat meals wisely, so that it will be easy to gather up the leftover ĥametz and dispose of it. After this, the ĥametz must be nullified; the bitul must be recited by the end of the fifth hour of the day.
Those who customarily perform hagala on their false teeth should do so on Friday and not eat any hot ĥametz food with them on Shabbat. Those who suffice with brushing their teeth should brush them thoroughly after the second meal (see above 11:12).
Se’uda shlishit, the third Shabbat meal, presents a problem: it is forbidden to eat ĥametz after the fourth hour of the day, and matza is forbidden the entire day. As a result, the obligation to eat a third meal is met by eating meat and fish or various fruits (SA 444:1). One may also eat matza balls, and according to many authorities, one may eat matza that has been thoroughly cooked, though some have a custom not to eat gebrokts on Pesaĥ (see above 8:2). One must avoid eating excessively during the third meal so that the matza of Seder night remains appetizing. Those who wish to destroy all of their ĥametz before Shabbat have options, explained in the notes. 1
Ta’anit Bekhorot is moved forward to Thursday, the twelfth of Nisan (SA and Rema 470:2). As mentioned, the custom nowadays is to arrange a siyum instead of fasting (see above 13:5). One should prepare the needs of the Seder – such as cooking the meal, preparing the ĥaroset, maror, and shank bone, and then freezing or refrigerating them – on Friday. They should not be taken out of the refrigerator until after Shabbat, as it is forbidden to prepare on Shabbat for Yom Tov. If preparations were not made before Shabbat, they must be prepared after Shabbat. However, this is less than ideal, as it may delay the Seder. Similarly, one may not set the Seder table on Shabbat. Rather, it should be set immediately upon the conclusion of Shabbat.
Two sets of candles should be set up before Shabbat: one for Shabbat and one for Yom Tov, as it is forbidden to stick candles on candlesticks with melted wax on Yom Tov. If one did not prepare them in advance, he may wedge them into the candlesticks without melting them in place.
^ 1.. Egg matza or matza ashira is made out of flour that was kneaded with fruit juice, which does not become ĥametz. The Sephardic custom is to permit eating it on Pesaĥ, while the Ashkenazic custom is to forbid (see above 8:1). According to all customs, matza ashira can be used for the first two Shabbat meals, but in such a case one must be kovei’a se’uda ("establish a meal") by eating four egg-volumes (ke-beitzim) of egg matza and by eating a fully satisfying meal. This will change the berakhot on egg matza from "mezonot" and "Al Ha-miĥya" to "ha-motzi" and "Birkat Ha-mazon" (see Peninei Halakha: Berakhot 6:4). If matza ashira was baked with a reliable process (see above 13:7), Sephardim may use it for se’uda shlishit, but it should be eaten before plag ha-minĥa (c. three seasonal hours before sunset). According to Ashkenazic custom, matza ashira may not be eaten after the fourth hour of the day (SHT and Igrot Moshe, in contrast to AHS, which permits eating it on Erev Pesaĥ, until the beginning of the holiday).
Cooked matza: Another option is to cook a whole matza. According to most opinions, one may eat cooked matza on Erev Pesaĥ, since it has been fundamentally altered and one would not fulfill the mitzva of eating matza on Seder night with such matza. Because it constitutes at least a kezayit, its berakhot are still "ha-motzi" and "Birkat Ha-mazon" and consequently one may use it to fulfill the obligation to eat three Shabbat meals. This is the ruling of MB 471:20 and SHT 19 ad loc., AHS 444:5, and Yeĥaveh Da’at 1:91 n. 10. SHT 471:20 mentions in the name of SAH and Ĥayei Adam that frying is the same as cooking, and that Pri Megadim equivocates. On the other hand, MA 444:2 asserts, citing Maharil, never having seen anyone adopt the practice of eating cooked matza at se’uda shlishit, and Gra implies that it may not be eaten on Erev Pesaĥ. Those who wish to follow the majority ruling and fulfill their obligation with cooked matza may do so (see SHT 444:1 and above 13:7). MB 444:8 raises the idea of splitting the second meal into two, but this is not ideal, as se’uda shlishit should be eaten after midday.