Preheat oven to 350°. Spray a 9x13 pan with non-stick cooking spray.
In a blender, pulse butter, onion, cream of mushroom soup, and chicken base several times to chop onion. Add sour cream, milk, salt and pepper, and pulse just until almost smooth. Stir in dried parsley.
In a very large bowl, combine the hash browns and cheddar cheese. Add the cream sauce and stir until it’s well combined. Pour into 9x13 pan and smooth the top.
Prepare topping: Mix panko crumbs, potato chips and melted butter in a Ziploc bag until well combined. Sprinkle evenly over the top of the casserole.
Bake uncovered for 1 hour until the sauce is bubbling and the topping is golden brown.