Crisp on the outside and cheesy on the inside.
, or creamy roux-based sauce, serves as the base for the casserole alongside thawed frozen shredded hash browns. A cup of sour cream adds a tangy silkiness to the mix, which counters the starchiness of the potatoes.
Looking for a crispier top on your hash brown casserole? Mix in all of the shredded cheddar cheese instead of reserving some for the topping, and the casserole should come out with a beautiful golden brown crust.
The casserole can be made up to two days ahead and reheated just before serving. To do so, bake it until bubbling but not browned on top—about 10 minutes shy of the cooking time. Let cool, then cover and chill. To serve, heat in a 350° oven until bubbling and browned on top. This family favorite can also be cooked completely and cooled, cut, and frozen to be reheated and enjoyed by the slice later on.1 small onion, finely chopped or coarsely grated2 tsp. Diamond Crystal or 1¼ tsp.
in a slow, steady stream, whisking constantly until combined. Bring to a simmer, still whisking constantly, and cook until béchamel is thickened to the consistency of a thin pudding, about 4 minutes. Transfer to a large bowl.