Champ (Mashed Potatoes from Ulster)

Place potatoes in a saucepan and cover with cold salted water. Bring to a boil and cook, partially covered, until tender, about 15 minutes.

Meanwhile, combine leeks and milk in another saucepan. Bring to a simmer over low heat. Cook, partially covered, stirring occasionally, until the leeks are tender, about 15 minutes.

Drain the potatoes and return them to the pan. With a potato masher, mash until smooth. Stir in oil and the warm leeks and milk. Season with salt and pepper.