Preheat oven to 375°F and adjust rack to the middle position. Spread macaroni evenly in a greased 13 x 9-inch baking dish. In a bowl, whisk 2 cups water, evaporated milk, dry mustard, salt, and pepper, then pour over the macaroni and stir to combine.
Cover the dish tightly with greased aluminum foil and bake for about 30 minutes, stirring occasionally, until the pasta is nearly tender and most liquid is absorbed.
Remove dish from oven and stir macaroni thoroughly, making sure to scrape the sides and bottom. Stir in remaining ½ cup water, shredded cheddar, and American cheese. Cover and bake for 5 to 8 minutes until the pasta is fully tender and the cheese is melted.
Remove the dish from the oven and stir to coat pasta evenly in sauce. Let cool while preparing the topping. Toss panko with olive oil in a bowl and microwave for 2 to 4 minutes, stirring occasionally, until golden brown. Let cool for 5 minutes, then stir in Parmesan and parsley. Sprinkle over the casserole before serving.
Keyword baked mac and cheese with crispy topping, creamy mac and cheese casserole, easy one-pan mac and cheese, one-pot mac and cheese, simple homemade mac and cheese