Nutrition per serving may change if servings are adjusted.
3 pounds Yukon Gold potatoes (about 12 medium)
1 tablespoon salt
2 tablespoons butter
4 cups halved and thinly sliced leeks (about 2 large; see Tip), white and light green parts only
1 cup buttermilk
Black or white pepper to taste
Peel potatoes, if desired, and cut into 2-inch chunks. Place the potatoes and salt in a large heavy saucepan. Add cold water to cover by 2 inches. Bring to a boil. Reduce heat to simmer, cover, and cook until potatoes are very tender, 10 to 15 minutes. Drain well.
Meanwhile, melt butter in a large skillet over medium heat. Add leeks and cook, stirring, until soft and beginning to brown, 4 to 8 minutes.
Transfer the potatoes to a large bowl. Mash with a potato masher, an electric hand-held mixer or by working through a ricer.
Stir the leeks, buttermilk and pepper into the mashed potatoes.
Make Ahead Tip: Transfer to a slow cooker, cover and keep on the “warm” setting for up to 2 hours.
Tip: To clean leeks, trim off green tops and white roots and split lengthwise. Place in plenty of water and swish around to release any sand or soil. Drain. Repeat until no grit remains.