Preheat oven to 180°C/350°F if using the oven for other roasting or 200°C/400°F if just roasting potatoes on their own (see notes). Place the goose or duck fat into a large roasting tin and place it in the oven to heat up.
4 tablespoons goose or duck fat
Peel the potatoes and cut them into large, even pieces (2-3 inches). Rinse and drain the potatoes.
3 pounds Maris Piper potatoes
Add your prepared potatoes to a large saucepan and cover with freshly boiled water from the kettle. Season the water generously with salt. Parboil these potatoes for 8-12 minutes until a knife penetrates about ¼ inch into the potato. They will still be firm in the centre. Drain the potatoes and add back to the pan. Leave to steam for 3-4 minutes.
Rough up the potatoes by shaking them gently in the pan. The surface will start to fluff up. This is exactly what we want.
In a small bowl, combine the polenta, chopped rosemary, salt and pepper.
¼ cup polenta, 1-2 tablespoons finely chopped rosemary, 1 ½ teaspoons kosher salt, ¼ teaspoon freshly ground black pepper
Toss the shaken potatoes with the olive oil and the polenta mixture until well combined.
1 tablespoon olive oil
Remove the tray with the goose fat from the oven and add the prepared potatoes. Toss to gently coat the potatoes in the fat. Add some extra rosemary sprigs if desired.
extra rosemary sprigs
Roast in the oven for between 55-75 minutes depending on the temperature you are roasting at. (55-65 minutes for 200°C/400°F or 65-75 minutes for 180°C/350°F). Turn the potatoes and baste with any fat half way through. Serve immediately.