The Food Lab: Better Home Cooking Through Science

 Add the fat and a   few generous    grinds  of  pepper  to  the

hot potatoes and toss well; the potatoes should end up
with a thin coating of potato-fat paste. Spray two rimmed
baking sheets with nonstick cooking spray (or coat with a
thin layer of oil). Transfer the potatoes to the baking
sheets and roast until the bottoms are crisp, rotating the
pans halfway through cooking, about 25 minutes. Test
the potatoes by trying to pry one or two pieces off the
baking sheet with a stiff metal spatula. If they don’t come
off easily, roast for additional 3-minute increments until
they do.