For a tender, fluffy challah, we borrowed a technique used to make Japanese milk bread, famed for its feathery-light crumb. We make a water roux (also called tangzhong) by mixing a little flour and hot water until it forms a gel-like paste; this increases the hydration level without turning the dough wet, provides structure to the crumb, and gives it that feathery-ness we love about milk bread. (It also increases the shelf life.) Oil is the fat of choice in traditional challah; we chose EVOO for