Good afternoon.
On the Insights page to Berachos 40 (see below) the Halacha quotes Mishna Berura s'if katan 38, but that was explaining the Mechaber. The actual Halacha seems to be in s'if katan 41 where he is explaining the Rama and he says one is not allowed to interrupt.
Kol tuv
>>INSIGHTS INTO THE DAILY DAF
Berachos 40
1) HALACHAH: "BRING THE SALT"
QUESTION: Rebbi Yochanan rules that one may interrupt between reciting the blessing for bread and eating the bread in order to say, "Bring the salt," since salt is necessary for the consumption of the bread because it adds taste to the bread. The Gemara relates that Rava bar Shmuel did not wait for salt before he ate his bread. He explained that since his bread was already tasty, it did not need salt. TOSFOS (DH Havei Melach) writes that our breads, too, are already tasty and do not need salt. Does this mean that we may not interrupt between reciting the blessing for bread and eating the bread in order to say, "Bring the salt"?
ANSWER: The MISHNAH BERURAH (OC 167:38) says in the name of the Acharonim that even though our breads are tasty and do not need salt, if one desires to eat his bread with salt (or another spice) it is considered necessary for the bread and he may interrupt to say, "Bring the salt."<<
Actually there is no Machlokes between the Mechaber and the Rem"a. They both agree that l'Chatchila one should not make any interuption between the Berochah and the eating, even for salt for Pas sh'Eino Naki, and they both agree that b'Diavad one does not repeat the Berochah for anything that was m'Inyanei d'Seudah, even for salt for Pas Nekiah. This is clear from the wording of the Mechaber which is a b'Diavad formulation (past tense).
Kol Tuv,
Yonasan Sigler