Nutrition per serving may change if servings are adjusted.
5 cups chopped mixed mushrooms
3 tablespoons chopped shallots
1/4 cup extra-virgin olive oil
1/2 teaspoon black or white pepper, plus more to taste
1/4 teaspoon salt, plus 1 tablespoon, divided
2 tablespoons dry sherry
3 pounds Yukon Gold potatoes (about 12 medium)
1 cup buttermilk
Preheat oven to 425 °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.
Make Ahead Tip: Transfer to a slow cooker, cover and keep on the “warm” setting for up to 2 hours.
Cut Down on Dishes: A rimmed baking sheet is great for everything from roasting to catching accidental drips and spills. For effortless cleanup and to keep your baking sheets in tip-top shape, line them with a layer of foil before each use.