Creamy, cheesy scalloped potatoes are a holiday favorite, adding comfort to any festive meal. With layers of cream, potatoes, onions, and cheese, all baked to golden perfection, this classic dish is a must-have for the Christmas spread. Serve it as the ultimate side to make your holiday feast feel complete and cozy.
Preheat the oven to 400º F. Butter a 3-quart, 2 ½-inch deep gratin dish
Melt 2 tablespoons of the butter in a skillet set over moderately low to medium heat. Add onion to skillet; cook and stir until the onion is soft. Set the cooked onions aside.
Pour the cold milk into a wide saucepan. Heat the milk, stirring frequently, until it scalds (when tiny bubbles appear around the outside of the saucepan).
While the milk is heating, melt 6 tablespoons of the butter in a heavy saucepan set over moderately low to medium heat. Place the flour into the saucepan with the melted butter and whisk for about 3 minutes. Slowly whisk in the scalded milk; bring the mixture to a boil. Reduce heat to a simmer and whisk the mixture for 1 minute more. Add salt and pepper to taste.
Place ⅓ of the milk mixture into the bottom of the gratin dish. Add ⅓ of the potato slices to the dish, slightly overlapping the slices. Place ⅓ of the onions atop the potato slices. Evenly top onions with ⅓ of the Cheddar cheese. Repeat the layers in the same manner two more times: milk mixture, potatoes, onions, and Cheddar. Sprinkle the last layer of cheese with bread crumbs. Cut the remaining 1 tablespoon of butter into small pieces and dot the bread crumbs with the butter pieces. Cover the dish with foil and place it in the oven. Cook the potatoes for 20 minutes, and then remove the foil and continue baking the potatoes until golden, about 30 to 35 minutes more.