make-ahead mashed potato casserole

Recipe adapted from Cook's Illustrated

Ingredients

Casserole
5 pounds russet potatoes (about 9 medium), peeled, sliced into 3/4-inch-thick rounds, and rinsed thoroughly
2 1/2 cups whole milk , warmed
1 cup sour cream
8 tablespoons unsalted butter (1 stick), melted
1 teaspoons Dijon mustard
1 medium clove garlic , minced or pressed through a garlic press (about 1 teaspoon)

8 ounces shredded extra-sharp cheddar cheese (about 2 cups)

Instructions


1. Place the potatoes in a large Dutch oven and cover by 1 inch of water. Bring to a boil over high heat, then reduce to a simmer and cook until the potatoes are tender (a paring knife can be slipped into and out of the center of the potatoes with very little resistance), about 15 minutes.


2. Drain the potatoes in a colander. Set a food mill (or ricer) over the now empty, but still warm, saucepan. Working in batches, drop the potatoes into the hopper of the food mill and process the potatoes into the saucepan. Stir in the milk, sour cream, butter, Dijon, 2/3 of the cheese, and garlic until uniform. Season with salt and pepper to taste.


3. Spread the potato mixture into a 13 by 9-inch baking dish. Sprinkle the remaining cheddar cheese evenly over the top.


4. To Store: Cover the dish tightly with plastic wrap and refrigerate for up to 2 days.


5. To Serve: Adjust an oven rack to the middle position and heat the oven to 350 degrees. Remove the plastic wrap and cover the dish tightly with foil. Bake for 20 minutes. Remove the foil and continue to bake until the casserole is heated through.