I recently asked a question https://dinonline.org/2020/10/28/flour-from-challah-used-for-mezonos-cake/
and thank you for your answer , but I think there may have been a misunderstanding.
The dough I will use for the mezonos cake is exactly the same dough as the one I use for my challos- no difference at all.
You mentioned in you reply that I wouldn’t want the two doughs to mix, but that is incorrect – they are exactly the same dough .
The reason I asked the shayla is because part of the dough will have a hamotzi bracha and part will have a mezonos bracha and so I’m not sure if I can make a bracha on taking challah.
Correct. Right now you don’t care because they are the same. However after you seperate the doughs you wil add chocolate etc. to one of them, and then you would not want the two doughs to mix. Therefore it is still considered isah lichalek.