Set to 450°F. The high heat is non-negotiable — it’s what creates the crispy crust while the parboiling has already handled the interior.

Place potato chunks in a pot and cover with cold water. Salt the water generously and bring to a boil. Cook until a knife slides in easily but the potatoes aren’t falling apart — about 10 minutes. Starting in cold water ensures even cooking all the way through.

While the potatoes boil, combine duck fat, rosemary, and garlic in a small pan over medium-low heat. Let the aromatics gently steep in the fat. If the garlic starts to brown, lower the heat — you want it soft and fragrant, not toasted.

Drain the potatoes and return them to the pot over medium heat. Shake gently for 45 seconds to 1 minute until the surface moisture has cooked off. This is the step most people skip — don’t. Steam is the enemy of crispy.

Pour the infused fat into a large bowl, add the potatoes, season with salt and pepper, and toss well. The potatoes should rough up slightly and leave a thick starchy paste on the inside of the bowl — that roughness is what becomes the crust in the oven.

Spread in a single layer on a sheet tray — don’t crowd them. Roast at 450°F for 50–60 minutes, shaking the tray and turning potatoes every 10–15 minutes, until deeply golden and crisp on the outside and cooked through.