A. The custom:
Many are accustomed to braid the Challah in the shape of a key on the first Shabbos after Pesach. Others knead a key within the Challah dough on the first Shabbos after Pesach. Some record that the above custom is not followed by Chabad Chassidim.
B. The reason behind the custom:
On Pesach all the heavenly gates were open. After Pesach they are closed. The symbol of the key on the Challah is to show that we are opening the gates slightly through our honor of Shabbos, and Hashem will then open it fully for us. Alternatively, it represents the opening of the gates of Parnasa, as after Pesach the Mun stopped falling and we were required to fend for our own livelihood.
Is the key Challah sourced in Christian doctrines and thereby its custom should be abolished?
Although some self-acclaimed historians argue that the custom of making key shaped, or key filled, Challah’s is also sourced in Christian or even pagan culture, and should hence be banished from amongst Jewish tradition, practically, the above custom is an authentic Jewish custom that may and should be honored by those who traditionally abide by it. The Halachic criteria of banning an activity due to idolatry or Darkei Emori is not satisfied by simply drawing historical sketches of a similar custom to that of other societies, as aside for the burden of proof to historically conclude that the innovation originated from those, and not Jewish, cultures, an action that contains a permitted logical symbol and representation which was never originated for the sake of idolatry is permitted to be adapted by Jews even if it originated from gentiles. Certainly there is no issue of Darkei Emori for one to perform an action customarily done by Jews for righteous reasons, even if there are gentiles who do so for the wrong reasons, as he is doing it to mimic his Jewish tradition and not that of the gentiles. This is aside for the Talmudic and Halachic dictum of “Minhag Yisrael Torah Hi” and thus certainly a custom which has been handed from generation to generation, and mentioned in Sefarim of Tzadikim, and is done for specially Kosher and Jewish oriented reasons, does not need any further defense or legitimization to legalize its continuity. We find many precedents of Jewish customs that can be argued to be considered Darkei Emori and are nonetheless traditionally done, and defended by the great Poskim, Rishonim and Achronim. Accordingly, we humbly suggest that historians [especially those who are self-acclaimed] stick to their field and not try to spread Halachic conclusions based on their ignorance of the workings of Halacha, and the criteria’s needed to be met in order for a matter to be forbidden. Whatever the case, as in all matters of Jewish law, this is an issue that requires arbitration from a licensed and practicing Posek and not an amateur who claims to specialize in the field of history.
May one cut a key shaped Challah on Shabbos?
There is no erasing prohibition involved in cutting a key shaped Challah on Shabbos.
Reciting Pirkei Avos:
It is accustomed to recite Pirkei Avos on every Shabbos between Pesach and Shavuos. Some are accustomed to continue reciting it after Shavuos, throughout the summer months, until Rosh Hashanah. [Practically, the Chabad custom is to say Pirkei Avos until Rosh Hashanah. On the Shabbosim which are in approximation to Rosh Hashanah, two chapters of Pirkei Avos are read, in order to complete the cycle prior to Rosh Hashanah.]
Reciting “Kol Yisrael…” prior to each chapter and “Rebbe Chanania Ben Akashyia…” at the end of each chapter: One is to recite the Mishnaic saying of “Kol Yisrael…” prior to beginning the chapter of Pirkei Avos. At the conclusion of the chapter one is to recite the teaching of “Rebbe Chanania Ben Akashyia.” [On the Shabbosim which are in approximation to Rosh Hashanah, in which two chapters of Pirkei Avos are read, some write one is to read the above opening and closing statements before and after each individual chapter. Others write it is only to be said once; the opening statement at the beginning of the first chapter and the concluding statement after concluding the second chapter. Others write that by the first four chapters that are said together [1-2 and 3-4], one reads the opening statement at the beginning of the first chapter and the concluding statement after concluding the second chapter. However, by the last two chapters [5-6] one reads the opening statement at the beginning of the first chapter and the concluding statement after concluding the second chapter.]
Learning one Mishneh in depth each Shabbos:
It is proper to learn in depth at least one Mishneh of the weekly chapter in Pirkei Avos. One is to learn this Mishneh together with its commentaries.
 Nitei Gavriel 39:1 writes that the custom is to shape the Challah like a key. The wording of the custom in Taamei Haminhagim is “Minakdim es Hachalos Bemafteichos”. It is unclear as to the meaning of this word Minakdin. It comes from the word Nekuda which means vowel. Seemingly this word refers to the shape of the Challah.
 Imrei Pinchas 298; Oheiv Yisrael [of Rav Avraham Yehoshua Heshel of Apta] Likkutim on Pesach; Taamei Haminhagim 596-597; Kol Naftali Megillas Rus p. 62; See Olas Moed Shevi’i Shel Pesach; Nitei Gavriel ibid
The reason behind the custom: On Pesach all the heavenly gates were open. After Pesach they are closed. The symbol of the key on the Challah is to show that we are opening the gates slightly through our honor of Shabbos, and Hashem will then open it fully for us. Alternatively, it represents the opening of the gates of Parnasa, as after Pesach the Mun stopped falling and we were required to fend for our own livelihood. [Oheiv Yisrael of Rav Avraham Yehoshua Heshel of Apta]
 Otzer Minhagei Chabad p. 243; Some report of an answer of the Rebbe stating that it is not our custom to do so. I have not seen this answer.
 Oheiv Yisrael of Rav Avraham Yehoshua Heshel of Apta
 See Rama Y.D. 178:1 “This is only forbidden if the clothing of the gentiles are worn by them for sake of frivolity [pritzus] or it is a gentile custom that has no logic behind it, as in such a case there is room to suspect that the custom derives from the Emorite customs, and that it derive from practices of idolatry passed down from their forefathers.”; Maharik 88; See Kapos Temarim Yuma 831 and Chavos Yair 234 that Darkei Emori applies towards practices that the gentiles developed as a result of idolatry, that they believed that these actions invoke their G-ds to give assistance. See also Ran on Shabbos 67a; See Admur 301:33 “Any medical treatment that works in accordance to Segulah [i.e. supernatural causes] rather than natural cause and effect [i.e. scientifically based] does not contain the prohibition of Darkei Emori so long as it is recognizable [to the onlookers] that it’s intent is for the sake of healing”; See Igros Moshe E.H. 2/13; Y.D. 4/11-4; O.C. 5/11-4
 See Admur 180:6 [not covering knife on Shabbos]; 432:11 [scattering 10 pieces of bread]; 452:4 [Hagalah]; 494:16 [Dairy on Shavuos]; M”A 494:6; Tosafus Menachos 20b
 See Rama 605:1 regarding Kaparos
 So rules Chazon Ish 61:1, brought in Piskeiy Teshuvos 140:4
 Siddur Admur
 There are six Shabbosim between Pesach and Shavuos corresponding to the six chapters of Pirkei Avos. The reason for saying Pirkei Avos between Pesach and Shavuos is as a preparation for Matan Torah.
 Sichas Parshas Naso 1982 [Hisvadyus 3:1633]; So was the custom of the Rebbe Rashab. [Rebbe in Reshimos brought in Otzer p. 244]
Background: The widespread Chabad custom until the year 1978 was to learn Pirkei Avos up until Shavuos and not onwards. However, from 1978 and onwards, based on a Sichah of the Rebbe on the Shabbos after Shavuos, the custom became to say Pirkei Avos also on the Shabbosim after Shavuos.
 Siddur; Admur in 54:4
The reason: The reason we conclude with these verses is because it is customary to recite Kaddish after Pirkei Avos, and we do not recite Kaddish unless we read a teaching that contains a verse or an expoundation of a verse. [Admur 54:4]
 Otzer Minhagei Chabad p. 246 based on Sichas Netzavim Vayeilech 1987
Background: The Rebbe in Sichas Parshas Seitzei 1981 plainly mentioned that the custom is to say it only once. However, in later years, the Rebbe publically debated whether it should be said once or twice. [See Hisvadyus 1985 5:2887; Hisvadyus 1987 4:352; Hisvadyus 1989 4:279; Sefer Hasichos 1990 2:681; Sefer Hasichos 1991 2:797] This led to a variety of opinions on this matter.
 Hiskashrus 946 based on Sichas Parshas Seitzei 1981
 Siddur Tehillas Hashem Kehos Eretz Yisrael based on Hisvadyus 1990 4 page 259 footnote 104 and Hisvadyus 1987 4 page 400
 Sichas 1991 2 p. 597