For the uninitiated, leaf lard is a very particular type of lard. It is lard rendered exclusively from the “leaf fat” of a pig. It is fat that is deposited around the kidney of the animal. Why is this important? Well, this fat has a different structure than other fat, which lends itself beautifully to pastry applications.
“Because of its large crystalline structure, it works exceptionally well in biscuits and pie crusts…Lard is somewhat soft even when cold, so when making a pie dough, some of the fat coats the flour, inhibiting much of the gluten development. The remaining fat, which stays in larger flakes, melts at a slightly higher temperature than butter, keeping the layers of flour and water separate. This also allows what little water is in the dough to turn to steam and separate the layers further. This is what creates a pie crust’s flakiness. “ The King Arthur Baking Company website.