Since the custom is to recite the berakha of Leishev before eating, the question arises as to which berakha to recite first – the berakha on the food or Leishev? According to Ashkenazim and some Sephardim, one recites the berakha over the food first, followed by Leishev. Since it is the eating that obligates us to sit in the sukka, the berakha on the food comes before the berakha on the sukka. One need not stand when reciting the berakha. The custom of some Sephardim is first to recite the berakha of Leishev while standing, and then sit down and recite the berakha over the food. People should continue their family’s tradition.
If one forgot to recite Leishev before eating, he should recite it in the middle and continue to eat. If he remembered only after he was basically finished eating, then if he can eat or drink a bit more before reciting Birkat Ha-mazon, he should recite Leishev and then eat or drink something. If he remembered after the meal was over, according to most poskim he should recite the berakha even though he does not intend to continue eating (MB 639:48); Sephardic practice is not to recite the berakha (Yeḥaveh Da’at 5:48).
As long as one remains in the sukka, the berakha he recited at the beginning of his time there covers him. Even if he eats an additional meal, he does not recite an additional Leishev. If he left temporarily – for example, to go to the bathroom, to bring something to the sukka, or to chat with friends – he does not repeat the berakha on his return, as the original berakha is still in force (MB 639:47). However, if he left for something significant – for example, to go to the synagogue or to take care of his business – when he returns, he must recite Leishev again. Even if he left for a trivial reason, if he was gone for more than an hour, he should recite the berakha again (SAH 639:13).
If one began a meal in his sukka and planned to continue with the meal in his friend’s sukka, then if his intention when reciting “ha-motzi” was to cover what he would eat at his friend’s, he also exempted himself from reciting Leishev in his friend’s sukka. If he did not have this in mind, before leaving his sukka he must recite Birkat Ha-mazon, and afterward he must recite all the berakhot again in his friend’s sukka.
. According to Baḥ and Taz (639:20), if someone recites Leishev before a meal and then remains in the sukka continuously until his next se’udat keva, he recites a Leishev again, as we assume that he intended his first berakha to cover only until the next meal. However, according to Levush, Shlah, and Magen Avraham (ad loc. 17), he does not repeat the berakha, since the sukka never left his consciousness. This is also the position of SAH, Ḥayei Adam, MB (ad loc. 47), and SHT (ad loc. 86). The halakha follows this latter position, as we are lenient when it comes to uncertainty about reciting a berakha. If someone enters the sukka and needs to recite Leishev for himself, he should be asked to have in mind the person who was still there from the previous meal. Some say that if one left the sukka briefly, even though his short absence is not considered an interruption, he must recite Leishev again when he is about to start an additional se’udat keva (Ya’avetz; Bikurei Yaakov). Others say that even in this case, he does not recite the berakha again (Derekh Ha-ḥayim; SAH; and others). Since the requirement of reciting a berakha here is uncertain, we do not recite it (SHT ad loc. 86).
. According to Magen Avraham and Shulḥan Arukh Ha-Rav, if one went to his friend’s sukka in the middle of a meal, he must recite Leishev again there. However, according to Taz and Levushei Serad, if he intended to go when he recited Leishev, he need not recite it again. MB 639:48 and SHT ad loc. 93-94 conclude that he should not recite the berakha. If one left his sukka after having finished his meal and having recited Birkat Ha-mazon, then presumably he did not intend for his Leishev to cover a visit to his friend’s sukka. Therefore, should he wish to eat there, he recites Leishev. See Peninei Halakha: Berakhot 3:11 regarding one who wishes to continue his meal at his friend’s home.