1bag(28 to 32-ounce) shredded frozen hashbrowns(defrosted)
1cupdiced onion
¼cupall-purpose flour
1cupmilk(preferably whole)
2cupschicken or vegetable broth(preferably low-sodium)
1cupgrated Monterey Jack cheese
1cupgrated sharp cheddar cheese
1cupsour cream
2cupcornflakes or potato chips(lightly crushed)
¼cupgrated Parmesan cheese
Kosher salt and freshly ground pepper (to taste)
Sliced chives (to garnish; optional)
Instructions
Preheat the oven to 350 F. Grease a 9x13-inch baking pan or spray with nonstick cooking spray.
Melt 6 tablespoons of the butter in a large, deep skillet over medium heat. Add the onions and cook, stirring occasionally, for 5 minutes until they start to turn golden and tender. Sprinkle the flour over the onions and stir occasionally for another few minutes until the flour has incorporated and started to turn golden. Whisk in the milk and stir over the heat for a few minutes. Whisk in the broth, and bring the mixture to a simmer, whisking often, until it bubbles and starts to thicken.
Remove the skillet from the heat and gradually whisk in the Monterey Jack and cheddar until the mixture is smooth and the cheese is melted. Whisk in the sour cream, then stir in the potatoes. Transfer the mixture to the prepared baking dish.
Melt the remaining 2 tablespoons butter in a small saucepan. In a large bowl, combine the cornflakes or potato chips and Parmesan cheese, then pour over the melted butter and stir to combine everything well. Sprinkle the mixture over the potato mixture in the casserole.
Cover with aluminum foil and bake for 20 minutes, then remove the foil and continue baking for 20 minutes or so, until the edges of the casserole are bubbling and the top is golden brown. Let sit for 10 minutes and sprinkle with chives (if desired) before serving.
Notes
Rather than frozen potatoes, you can also use diced par-cooked potatoes, or you can parboil potatoes and then grate them instead. But if you’re looking for quick and easy, grab that bag of frozen hashbrowns.
The most classic toppings are cornflakes or lightly crushed potato chips, and those make for a terrific crispy top layer. You could also use Panko breadcrumbs, or crushed Ritz or other crackers.