There is a statement of Rav Yochanan in Maseches Challah Yerushalmi that is paskened in Shulchan Aruch 326:2 that if one makes enough dough that is beyond the shiur challah, but intends to "divide it", they are not obligated in the mitzvah of hafrashas challah. It is not clear what exactly the case is that this halacha is referring to. The achronim try to reconcile this with the practice that women have to make many small challas from the dough which has the shiur challah and make a bracha on their hafrashas challah. Why doesn't this qualify as העושה עיסה לחלקה בבצק פטורה? The Shach (5) and Taz (2) write that this halacha is limited to a case where it is being made for the purpose of dividing among many people AND that it will be distributed while still in the dough state. However, if one is baking many loaves of challah to be distributed among a group of people, but will be distributed after baking it is obligated in hafrashas challah. Certainly if one is baking it with the intention to divide it into smaller loaves that they will be keeping for themself, it is also obligated in the mitzvah of hafrashas challah.
However, both the Pischei Teshuva in citing the Beis Ephraim and the Tzlach in our sugya point out that from Tosafos quoting Rabbeinu Yechiel, this doesn't seem to be true. Tosafos implies that anytime the dough which has a shiur challah is going to be divided up and then baked as separate loaves, even if it will all belong to one person, he questions whether there is a mitzvah of hafrashas challah (so that no bracha should be made). According to Tosafos, whenever a woman bakes challah for shabbos and makes multiple loaves so that there will be lechem mishna, there is no bracha made on the hafrashas challah. The Tzlach struggles trying to justify the minhag that women have to make a bracha, with this approach of Tosafos.
The Madanei Yom Tov (also cited by Pischei Teshuva) suggests that if she is dividing it to bake a little now and a little at some later point (for example she is freezing some of the dough), she may not be obligated in hafrashas challah. But, if her intent is to bake everything now, she is obligated in this mitzvah. The Tzlach says that this also doesn't read well into Tosafos because Tosafos should have mentioned that the safeik of whether it is obligated in hafrashas challah is because sometimes it isn't all baked at one time.
The Tzlach understands Tosafos simply that if the loaves are divided while they are dough there is no mitzvah of hafrashas challah. But offers two approaches to justify the minhag to be mafrish challah with a bracha.
1. There is a machlokes rishonim whether we pasken like Rav Yochanan to exempt from challah when dough is divided. The Rambam paskens like R. Yochanan, but the Ra'avad doesn't. There is also a machlokes as to whether the oven can combine the loaves to create an obligation. Therefore, we have a s'feik s'feikia obligating in the mitzvah of challah, and are entitled to make a bracha on the hafrasha. Although one is being mafrish with a bracha in the state of dough before they even enter the oven, the fact that one intends to put them in the oven in a way that they may combine, makes it that they are not considered דעתו לחלק and is obligated in the mitzvah of hafrashas challah.
2. The nature of this exemption of דעתו לחלק is that when one divides the dough and intends to distribute it among many people, it is unlikely to ever come back together and therefore exempt. It doesn't really matter whether it is being given out to others or kept for oneself. So long as the chances of it coming back as one unit is very slim, it is patur from hafrashas challah. Normally, when one doesn't distribute to others we are concerned that they different loaves will come back together in one basket and be obligated in challah, therefore even now the separating into separate loaves doesn't exempt. Tosafos is speaking about a type of bread that is going to be sufganin in the end (meaning it will be made in a way that there is excessive oil and shouldn't be subject to challah). The only reason to subject them to challah is because now they are all in one dough and we pasken תחילתו עיסה וסופה סופגנין חייבין. Therefore, if one intends to separate them into separate loaves, it is now exempt and later will never become obligated because later it will be sufganin which are exempt from challah.