Peel the Maris Piper potatoes and cut them into roughly even-sized chunks.
Place them in a large saucepan and cover with cold water. Add a generous pinch of salt.
Bring the water to the boil, then simmer the potatoes until the outside is tender but the centre still has some firmness. You don't want them completely cooked at this stage.
Drain the potatoes thoroughly and allow them to steam dry for a few minutes.
Return them to the saucepan or place them in a colander and give them a good shake to rough up the edges.
Season with salt and black pepper.
Preheat the oven to 200°C fan / 220°C conventional / Gas Mark 7.
Add the duck fat to a large roasting tray and place it in the oven for 10 minutes until it heats. The fat should be very hot before adding the potatoes.
Carefully add the potatoes to the hot duck fat and turn them so they're well coated.
Spread them out into a single layer, leaving plenty of space between each potato.
Roast for approximately 50–60 minutes, turning every 20 minutes during cooking, until deeply golden, crispy and fluffy inside.
Serve immediately while they're hot and crispy, with plenty of homemade gravy and your favourite Sunday roast.