Cheesy Hashbrown Casserole

unsalted butter, (melted)

kosher salt (some have noted it's a bit salty so I would start with 1 teaspoon..also keep in mind (KOSHER SALT [which is coarser], not table salt!))

ground black pepper

large onion, (finely chopped (white or yellow onion works))

: 10.5 ounce can of cream of chicken condensed soup

freshly grated Colby Jack cheese

frozen shredded hash browns, (thawed)