From Raymond Sokolov: Kosher laws don't permit the use of dairy fat (butter) with meat... [Jews had no] access to vegetable or olive oil [so they] turned to chickens. They produced their own flavorful meat-cooking fat... The richest deposit of chicken fat appears in the neck of a raw chicken. One chicken will not yield enough raw fat to be worth rendering; a fowl will give up barely enough. Harbor chicken fat in the freezer. When you have a substantial quantity, render it, as indicated below. The rendered fat also keeps well in the freezer. Although identical, I learned this recipe not from Raymond Sokolov, but from my mom, who learned it from her father (zichrono l'vracha).