Tuna Noodle Casserole with Potato Chip Topping

Name: Tuna Noodle Casserole with Potato Chip Topping
Ingredients: Kosher salt and freshly ground black pepper; 4 tablespoons unsalted butter, plus more for the baking dish; 1 medium onion, finely chopped; 8 ounces cremini mushrooms, sliced; 1/4 cup all-purpose flour; 2 cups whole milk; 1 cup chicken broth; 8 ounces medium pasta shells (about 3 cups); One 6-ounce jar Italian tuna in olive oil, drained and flaked; 2 tablespoons chopped fresh flat-leaf parsley; 2 cups grated sharp white Cheddar; 1 1/2 cups crumbled flavored potato chips, such as salt-and-vinegar, onion or jalapeno