Make-Ahead Creamy Potatoes

Directions

1. Place whole potatoes in a large stockpot; add water to cover. Bring to a boil. Reduce heat; cook, uncovered, until tender, 20-25 minutes. Drain.
2. Meanwhile, in a large saucepan, heat 1/4 cup butter over medium-high heat. Add mushrooms; cook and stir 2-4 minutes or until tender. Stir in flour until blended; gradually whisk in milk, salt, pepper and thyme. Bring to a boil, stirring constantly; cook and stir until thickened, 1-2 minutes.
3. Peel and cube potatoes when cool enough to handle. Press through a potato ricer or strainer into a large bowl; stir in cheddar cheese, sour cream, mushroom mixture, onion and remaining butter. Transfer potato mixture to a greased 13x9-in. baking dish. Refrigerate, covered, overnight.
4. Preheat oven to 375°. Remove potatoes from refrigerator; uncover and let stand while oven heats. Sprinkle with bread crumbs and Parmesan cheese. Bake, uncovered, until heated through, 55-65 minutes.