8 tablespoons (1 stick) salted butter
One 28- to 32-ounce bag frozen shredded hash brown potatoes
1 medium onion, finely diced
1/4 cup all purpose flour
1 cup milk
2 cups low sodium chicken broth
kosher salt and freshly ground black pepper
1 1/2 cups grated Monterey Jack cheese
1 cup sour cream
1/2 cup grated sharp Cheddar
2 cups kettle cooked potato chips
1/4 cup grated Parmesan
1. Preheat the oven to 350 degrees F. Grease a 9-by-13-inch baking dish with 1 tablespoon of the butter. Take the potatoes out of the freezer while you are preparing the rest of the ingredients.
2. Heat a large, deep skillet over medium-high heat, then melt 6 tablespoons of the butter in it. Add the onions and cook, stirring occasionally, until the onions start to soften, 3 to 4 minutes. Sprinkle the flour over the onions and stir to incorporate. Cook for a minute or 2 to cook out the raw flour, but do not let it color. Whisk in the milk, making sure to get out all the lumps. Add the broth and whisk again if there are still lumps. Bring the mixture to a simmer and allow it to thicken, about 3 minutes. Season to taste with salt and pepper. Turn off the heat and stir in the Monterey Jack, sour cream and Cheddar. Add the hash brown potatoes and mix everything together. Transfer the mixture to the prepared baking dish.
3. Melt the remaining 1 tablespoon butter in a small pan. Put the potato chips and Parmesan in a bowl and crush the potato chips. Pour in the melted butter and toss to coat. Sprinkle the crumbs over the top of the potatoes.
4. Cover with foil and bake for 20 minutes, then remove the foil and continue baking until golden brown on top and bubbling around the edges, about 15 minutes more. Let rest for 15 minutes before serving.