Do we say בישול מפעפע בכל הכלי (that when you cook in only part of the pot the cooking makes the food be absorbed throughout the whole pot) or not?
This is the question of “חם מקצתו חם כולו” do the blios spread throughout all of the pot or utensil. There are 2 opinions brought in SHulchan Aruch Y:D 94:1, the Rama there rules leniently. There is a debate as to the opinion of the Rama is that the blios do not reach the other part of the pot/utensil at all, or in fact they reach there, just they are not expelled when only the other part of the utensil is immersed in heat. According to the stringent opinion if one where to immerse a spoon halfway, we would say that when immersed again only blios from the bottom half will come out, but if it is flipped and the upper half is immersed, blios will be expelled from there as well. There is another extensive discussion as to what level of heat the utensil is being exposed to in which there the above debate and at which point all would agree the blios do or do not travel throughout, see Pischei Tshuvah and other commentaries ibid..