Preheat oven to 450F/232C.
Remove duck fat from refrigerator and bring to room temperature. Alternately, heat for 30 seconds in the microwave. The duck fat should be runny and pourable.
Cut potatoes into 1-inch chunks, leaving the skin intact. Place potatoes in a large stock pot and add cold water to cover. Bring to a boil. When the water comes to a boil, set a timer and boil for 5 minutes.
Drain potatoes in colander. Shake the colander to drain excess water. Set aside for 5 more minutes to continue steaming/draining.
Dump potatoes onto a sheet pan. Drizzle with duck fat. Sprinkle with salt and pepper. Mix well with hands and spread out in an even layer.
Roast until potatoes are crispy and browned, about 40-55 minutes. About halfway through, scrape up the potatoes with a spatula and turn them to the other side.
Garnish with parsley and a few more grinds of fresh pepper. Serve immediately.