Roasted Mushroom Mashed Potatoes

Preheat oven to 425 degrees F. Toss mushrooms and shallots with oil, 1/2 teaspoon pepper and 1/4 teaspoon salt. Spread on a large baking sheet. Roast until brown and caramelized, 20 to 30 minutes. Remove from the oven and immediately sprinkle with sherry. Stir well.

Meanwhile, 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.

Transfer the potatoes to a large bowl. Mash with a potato masher, an electric hand-held mixer or by working through a ricer.

Stir buttermilk and pepper to taste into the mashed potatoes. Stir in the roasted mushrooms or spoon them over the potatoes.