Gemara

Menasheh: We cut the bread from where it first forms a crust.

Berachos 39a (R. Chiya bar Ashi citing Rav): If dry bread was soaked in a bowl, its blessing is ha'Motzi.

He argues with R. Chiya, who said in the name of Rav that one must finish blessing ha'Motzi with (at the same time he breaks off from) the loaf.

The soaked bread is already in pieces (so one should bless on the loaf)!

Objection (Rava): Also the bread is sliced when the blessing is finished! Rather, one must finish ha'Motzi before breaking off from the loaf.

The Halachah follows Rava.

Rishonim

Rambam (Hilchos Berachos 7:2): One blesses ha'Motzi, finishes the Berachah and then cuts a slice.

Rambam (3): One cuts in the place where it was baked well.

Hagahos Maimoniyos (3): Sefer ha'Mitzvos says to cut from the bottom, for it gets baked first when it is stuck in the oven. This is the custom in France. In Ashkenaz, they cut from the top, for it cooks there first. My Rebbi would make one cut from both sides to fulfill both opinions.

Rosh (Berachos 6:19): If he has only the soaked bread, surely he blesses on it! If he has a full loaf, surely he blesses on it! Rather, he has a big loaf or big pieces, and he makes small pieces to bless ha'Motzi and eat. Rav teaches that he need not bless when cutting. Since he breaks then up in order to bless ha'Motzi and eat them, blessing afterwards is like blessing beforehand. Rav could have taught this about regular bread. He taught about soaked bread to teach that wept even if the pieces are too small to cut at the time of the Berachah. Rava teaches that one breaks off the piece after finishing the Berachah. Due to Rava, some do not cut it before the Berachah. This is improper. It is like an interruption to cut between the Berachah and eating. Rather, he cuts but does not break it off until after the Berachah. He should initially cut a little, so that if he holds the slice, the rest of the loaf will come with it. If not, it is like a slice. This is like R. Yehudah in Tevul Yom (3:1); the Halachah follows him.

Poskim

Shulchan Aruch (OC 167:1): One cuts the bread in the place where it was baked well.

Kaf ha'Chayim (2,3): Normally, we give precedence to what the one blessing prefers. Here is different, for we require the dearness of the bread. If he is old and cannot eat the hard part, he cuts where it is soft. If he blesses also for others, he cuts for himself where it is hard and for them where it is soft.

Rema: One should cut our bread on the side, and cut a little from the top and from the bottom.

Beis Yosef (DH va'Yivtza): Rashi explains that it forms a crust on top, at the sides, or on the bottom, but not in the middle. If he was given a piece, he cuts only from the bottom. Alternatively, it is where it first forms a crust. This is the same as the first version. Alternatively, it is where it finishes cooking, and not from the place called Beshul. The first version is primary. It seems that the Tur and Rambam hold like the last version. Maseches Derech Eretz Rabah (Perek 6, towards the end) says that one should not cut where it is soft, rather, where it is hard.

Darchei Moshe (1): Or Zaru'a says that he cuts opposite where the bread cracked. This is where it started to bake, and the pressure caused it to crack opposite this place.

Taz (2): The Gemara refers to their bread, which was baked (stuck to a wall of the oven) in the air of the oven. Both the top and bottom were baked in the air of the oven. Our bread is baked on the bottom of the oven. Some say that the bottom gets baked first, for there it is stuck to the oven. Some say that the top gets baked first. Therefore, to fulfill both opinions one cuts from the top and bottom in one cut.

Gra (2): It is not clear how our bread is different. The Taz is astounding.

Bi'ur Halachah (DH uv'Pas): In the days of the Gemara, the bread was baked stuck to a wall of the oven. The top (facing the air of the oven) and bottom (stuck to the wall) began to bake at the same time, so one could cut from either one. Our bread is baked on the bottom of the oven. Some say that the bottom gets baked first, for there is the fire. Some say that the top gets baked first, for it is in the air of the oven. Therefore, one cuts on the side, and cuts from the top and from the bottom. Levushei Serad and the Gra asked that this applies also to the bread in the days of the Gemara! How is our bread different? The Rema wrote Stam, but it is as if he wrote 'some say that...' The Acharonim bring the Rema, for this way we fulfill all opinions.

Kaf ha'Chayim (4): There is an argument (254:5) also about which part gets baked first regarding the bread in the days of the Gemara! The Rema means that our bread is thick, and one could cut only the top or bottom. He says to cut from the side to fulfill both. When cutting before the Berachah, one starts from the bottom, but leaves it looking whole on top.

Magen Avraham (1,2): The Mechaber rules like those who say that he cuts where it is baked best, i.e. it is hard. The Rema rules like those who say that he cuts where it begins to form a crust. One cuts our bread on top, like I wrote below (168:5). Maharal used to cut a ring around the bread (e.g. he would cut a little bit into the bread, and while the knife was inserted, rotate the bread or move the knife in a circle around, to cut it on all sides) but leave the middle connected, and (after ha'Motzi) he would break off the piece from bottom to top. For a wafer, he would place eight fingers above and two thumbs below, and bless and break it.

Mishnah Berurah (3): If part is burnt or dirt stuck to it, he should not cut there for ha'Motzi.

Shulchan Aruch (ibid): He cuts a slice. He must make a small cut, so that if he will hold the slice, the rest of the loaf will come with it. If not, it is considered a slice. He leaves it attached and begins to bless. After finishing the Berachah, he separates it, so the Berachah will finish when the bread is whole.

Beis Yosef (DH v'Yachtoch): The Avudraham rules like the opinion that he finishes cutting together with the end of the Berachah. This is a mistake.

Beis Yosef (DH v'Tzarich): Hagahos Maimoniyos (7:6) says that Rabbeinu Meir holds that if one holds the slice, and the rest comes with it, this is called whole. He says that R. Baruch says that we need not be concerned if not, for in any case he will break it off. We do not follow him against Rabbeinu Meir and the Rosh. Also, his reasoning is not sound.

Taz (3): If one did not cut until after the Berachah, this is not a Hefsek, for we do so on Shabbos. During the week (when we are not so concerned for a whole loaf) it is best to start cutting beforehand.

Magen Avraham (4): Even if one blesses on a piece, he should not cut it totally until after the Berachah, so it will appear larger.

Kaf ha'Chayim (4): If the soft or thin and one can break it quickly, he does not cut it until after the Berachah, so it will be truly whole.

Kaf ha'Chayim (5): If part is so burnt that it is inedible, some say to cut it off before blessing, and others disagree. One should bless on a different loaf if possible. If one can scrape it off and it will look whole, he should do so before the Berachah.

Kaf ha'Chayim (13): While blessing one may not cut or engage in anything.

Rema: On Shabbos he does not cut until after the Berachah, so the loaves will be whole. If he forgot and cut like during the week, it does not hurt.

Magen Avraham (5): The Mordechai says that the concern is lest the piece fall and he will not have Lechem Mishneh. This implies that if it did not totally fall, it is Lechem Mishneh. However, the Agudah says in the name of Maharam that this is only if when he holds the slice, the rest comes with it. The Rema connotes that if he cut more than during the week (i.e. if he held the slice, the rest would break off) it is like a piece. This is like Maharam.

Shulchan Aruch (168:3): If two buns stuck to each other, and part of one was cut off, he cuts it all off.

Rema: He does not cut (a slice for ha'Motzi) from where the other was removed, for there it looks like a slice, rather, from where it is (looks) whole.

Magen Avraham (5): Darchei Moshe says that also, where it is whole it began to form a crust. This is difficult. If so, we should cut every slice from the whole side for this reason! I did not see anyone do so. Rather, it suffices to cut it form the side of the bread, like it says in 167:1. This is why Maharil needed to say that from the side it looks like a piece. A piece looks like a piece from every side, so it suffices to cut it from the side.

Kaf ha'Chayim (16): Not seeing something is not a proof. One should cut from the whole side to fulfill all opinions.

Mishnah Berurah (167:3): One may cut a piece from the side where it was cut, as long as he cuts the top and bottom.