Heat oil in a skillet over medium-high heat. Brown pork chops 2 to 3 minutes per side, then set aside.
In a large bowl, combine sour cream, cream of chicken soup, and milk until smooth.
Add frozen hashbrowns, onion, cheddar cheese, salt, and pepper. Mix until evenly coated.
Spread hashbrown mixture into an ungreased 9x13 baking dish.
Lay browned pork chops on top in a single layer, pressing them slightly into the filling.
Bake uncovered at 375°F for 45 to 50 minutes, until the casserole is hot and pork chops reach 145°F internally.
Rest 5 minutes before serving.
Notes
Bone-in pork chops stay juicier during the long bake, but boneless chops work if you check them earlier. Use condensed soup straight from the can, not diluted. Store leftovers covered in the refrigerator for up to 3 days and reheat with a splash of milk or broth if the hashbrown layer looks dry.