Magen Avraham says that one is not supposed to eat bread to exempt himself from other berachos, if the bread isn’t desired and isn’t the main part of the meal. Does this apply even to pas haba b’kisnin? Meaning, would Magen Avraham say that one shouldn’t use bread if one has a safek concerning kevius seudah on pas haba b’kisnin – or is this case different?
One can and should eat an amount of bread to get out of the safek. For this case, a kezayis of bread would be sufficient.
There are two issues involved in making a blessing on bread in order to get out of a safek.
One issue the question of a berachah she’einah tzerichah: if one doesn’t want to eat bread, the blessing is unnecessary, and shouldn’t be made. In this case, because there is a halachic doubt as to whether there would be a kevius sedudah on pas haba bekisnin, it is permitted to eat the bread and make the extra blessing, because this serves to get out of the safek, and would not be considered an ‘unnecessary’ berachah.
A number of sources indicate that there is no problem of making a blessing (in this case, the blessing on bread, which one doesn’t want to eat) in order to get out of a halachic problem (of safek concerning pas haba b’kisnin). See, for instance: Magen Avraham 197:7; Peri Chadash, Yoreh De’ah 19; Mishnah Berurah, Biur Halachah 4, s.v. Alaihu; Or Le’Zion, vol, 1, no. 17; among others.
The second issue, which is mentioned by the question, is that bread only exempt other foods from their blessing because it is considered the main part of the meal. Therefore, if a person eats a small amount of bread alone, it is possible that the bread would not be considered the main part of the meal, and therefore it would not exempt the other foods from a blessing. Due to this concern, Magen Avraham (177:1) writes that one should not make a blessing on bread when one does not wish to eat bread, and only does so to exempt himself from other blessings. A similar concern is raised by Chayei Adam and Shulchan Aruch Ha-Graz. See also Mishnah Berurah 177:3, Aruch Hashulchan 177:2, and Kaf Hachayim 177:4. See, however, Shaarei Teshuvah, quoting from Even Ha’ozer (174).
The case in question, however, is different, in that the pastries themselves are a form of pas (bread), and the only question is whether or not they are considered a seudah (meal) or not. If one makes a blessing on bread, and immediately afterwards eats the pastries, this reveals one’s intention to eat the pastries as a se’udah, which automatically gives them the blessing of hamotzi.
Similar advice is given for Sefardim who wish to avoid doubts over the blessing for eating matzah (see Yaskil Avdi, 1:9:29).