Someone made a large amount of challas that had inside of it onions that were cut with a milchig knife (the onions were put into the dough and then baked that way.) Is this a problem of making a large amount of milchig challas that they would all be ossur to eat (al pi what it says in YD Siman 97 – since it’s a large amount and without a shinui?) And that these onions are ossur to eat together with baser?
It appears that the bread is fine. If one can, it is good to make a siman now.
According to the Magen Avraham, who is stringent concerning the passing on of the taam of a davar charif, the bread will apparently be forgidden. However, many poskim side with the Even Ha-Ozer, who dispute this position (though the Mishnah Berurah cites the Magen Avraham alone).
However, there is room to contend that even the Magen Avraham will not be stringent if the knife was not a ben yomo, as we have discussed several times before, and the bread will therefore not be considered as having been kneaded with milk.
In addition, there is a likelihood of having shishim in the dough against the taste of milk in the onions.
Although the onions are milky, the prohibition of bread will not apply if only the onions that are mixed with it are milky (see Kovetz Be’er Yosef, 5768, at length on this point).
Based on the Chochmas Adam (concerning milk that spilled onto bread after it was baked), there is still room to make a siman now, though there is room to make a distinction between the cases. See also Badei Ha-Shulchan 97:1.