Rav Asi quoting Rav: Small salted fishes are not forbidden due to bishul Akum.Rav Yosef: If a gentile broiled these fishes, they can be relied upon for Eiruv Tavshilin. But if the gentile cooked them as kosi d’harsena, it is forbidden due to bishul Akum [because the flour was not fit to eat previously].We might have thought that the fish is the mainstay of the dish, so we’re taught that the flour is actually the mainstay of the kosi d’harsena.
Tosfos: In mesichta Avodah Zarah we learn that another condition of bishul Akum is that it must be fit to be served at a dignified meal. The example given there is that small fishes are not fit to be served and would not qualify for bishul Akum?We must say that here we’re discussing fish that are slightly bigger. [Some poskim explain that there it is discussing fish that will grow big but are still small - those are not important. Here we’re discussing small fish that do not grow bigger, these are indeed considered significant enough to be affected by bishul Akum].
The Flour is the Mainstay: Based on this, we permit bread broiled with eggs, baked by gentiles. Since the bread is the mainstay, and gentile bread is permitted.We might want to differentiate between the cases: since here this concept is being used as a stringency, while over there it would result in leniency. But actually, here the Gemara is willing to use it as a leniency - if only the fish would be considered the mainstay. Since the flour is considered the mainstay it results in stringency but had the fish been the mainstay our Gemara would ruled leniently, so we can apply this principle to our egg-bread.We need not worry that the eggs are from non-kosher species since it is uncommon, neither do we need to worry about bloodspots which are not found in most eggs. Our practice of checking eggs for bloodspots is a stringency,, if they weren’t checked, they’re kosher. We also do not need to worry that the eggs are from neveilah or treifah chickens, since most eggs are not. 
This podcast has been graciously sponsored by JewishPodcasts.fm. There is much overhead to maintain this service so please help us continue our goal of helping Jewish lecturers become podcasters and support us with a donation: https://thechesedfund.com/jewishpodcasts/donate