Creamy Mushroom-Potato Bake

Directions

1. Preheat oven to 400°. Place potatoes in a large saucepan and cover with water. Add 1/2 teaspoon salt. Bring to a boil. Reduce heat; cover and cook until tender,10-15 minutes. Drain and mash (do not add butter or milk).
2. In a large skillet, saute onion and mushrooms in 2 tablespoons butter just tender, 3-4 minutes. Stir into potatoes along with sour cream, pepper and remaining salt. Spoon into a greased 2-qt. baking dish. Sprinkle with cheese; dot with remaining butter.
3. Bake, uncovered, until heated through and golden brown, 20-25 minutes.