THE GEMARA (A.Z. 38a) teaches that any food which can be eaten raw is exempt from the prohibition of bishul akum. Common examples of foods that are nechal chai include water, juice, milk, yogurt, cheese, oil, and many fruits and vegetables. Aruch Hashulchan (Y.D. 113:14) points out that foods that were edible raw but then dry out and become inedible can become subject to bishul akum.
The heter of nechal chai is true even if the food would be greatly improved through the cooking. So long as the food was considered edible before the cooking, it is permitted. For example, Rashba  explains that cooked porridge is permitted, because raw grains qualify as nechal chai. Rav Belsky points out that the examples in Shulchan Aruch of foods that are not edible raw are all foods that one would find distasteful to eat raw, such as eggs, flour, bitter dates, fish and meat. However, foods which are not distasteful, even if they are only on par with mai’chel Ben Drusai (a famous bandit who ate his food with the most minimal cooking possible), and even though most people would prefer to eat the food cooked, can still qualify as
nechal chai. Included in this category is fresh sweet corn.
Shulchan Aruch (Y.D. 113:12-13) says that if a non-Jew salted fish until it became edible, it would be permissible to allow him to
cook it afterwards. As mentioned above, in ascertaining whether a food reaches the level of edible, it is not required that it reach the level that most people would actually eat the food in this manner, but rather that they would find the food edible and not distasteful. Similarly, once a Yisroel cooks food until it is k’maichel Ben Drusai (barely edible) it is permissible to have a non-Jew finish the cooking. This is true even though most people do not eat the food in this manner.
Shulchan Aruch (Y.D. 113:2) says that if a non-Jew cooked a mixture that contained some ingredients that can be eaten raw and some ingredients that requires cooking, one needs to determine which ingredients are the ikar and which are tafel. If the ikar ingredients can be eaten raw then the food as a whole is viewed as edible raw and is exempt from bishul akum. If however, the ikar ingredients require cooking, then this food requires bishul Yisroel. If none of the ingredients are clearly the ikar ingredients, then we follow the rov (majority).
EXAMPLE: Kasa d’harsana (fish paste) is a mixture of flour (which requires cooking) and fish oils (which are edible raw). The Gemara (A.Z. 38a) says that since flour is considered the ikar, kasa d’harsana is subject to bishul akum.
EXAMPLE: Dough is kneaded with eggs, and baked by a non-Jew into bread. Tosfos (38a s.v. ka mashma lon) says that although the bread contains eggs, it is permitted as pas palter, since the ikar is the pas and the egg is tafel.
EXAMPLE: Meringues are made from sugar and beaten egg whites. Arguably, the ilkar of the meringue, both in purpose and in volume, is the sugar (which is considered nechal chai). Therefore, they are not subject to bishul akum .
Shulchan Aruch (Y.D. 112:6) extends this rule even to bread that is baked with a layer of egg on top. Since the ikar is the bread, which is permitted as pas palter, the egg cooked with it is permitted as well. This at first seems like a contradiction with what Shulchan Aruch (Y.D. 113:3) writes regarding dough baked with meat or fish, where we pasken that the knish is assur. Pri To’ar 112:9 explains that although the layer of egg is b’en, yet it becomes one with the bread, but the pieces of fish or meat remain completely separate entities from the bread, so they cannot be subsumed under the heter of pas palter.
However, Rema is machmir to not even consider the layer of egg as a ta’aruvos, since the layer of egg remains b’en (distinct). Aruch Hashulchan (Y.D. 112:21) though says that even Rema would be maikel to consider the egg a tafel if the egg just leaves a shine on the bread, as is commonly done to challah.
Example: French toast is made by soaking bread in egg and then frying it. The egg that is absorbed into the bread would be permitted because of ikar v’tafel. However, since there is also a layer of egg that remains on top of the bread, we require bishul Yisroel for French toast as per the chumra of the Rema.
by Rabbi Eli Gersten, RC Recorder of OU Psak and Policy
 Rashba A.Z. 38a. This is also the opinion of Rabbeinu Chananel, Ra’avad and Ritva
 However, Teshuvas Simchas Kohen Y.D. I:164 says that perhaps one should be machmir
with meringue, since once the egg is added to the sugar perhaps the entire mixture is no
longer edible raw, so even the sugar becomes subject to bishul akum. However, it does
not sound this way from Beis Yosef (113:2), who quotes Tashbeitz that confections that
contain honey and flour are permitted, since the honey is ikar, and the flour is just to