Yukon gold potatoes (about 6; peeled if desired), cut into 2-inch chunks
kosher salt and black pepper
(1 stick) unsalted butter, cut up
- Place the potatoes in a large pot and add 2 teaspoons salt and enough cold water to cover. Bring to a boil. Reduce heat and simmer until the potatoes are very tender, 20 to 25 minutes. Drain and return the potatoes to the pot.
- Meanwhile, heat the oil in a large skillet over medium-high heat. Add the mushrooms, thyme, and ½ teaspoon salt and cook, tossing occasionally, until tender, 6 to 8 minutes.
- Add the milk, butter, ½ teaspoon salt, and ¼ teaspoon pepper to the potatoes and mash to the desired consistency. Top with the mushroom mixture.