Heat oven to 400° F. Butter a casserole or 9-by-13-inch baking dish.
Cook the macaroni until almost tender but still firm, about 2 minutes less than the package directions. Drain and rinse under cold water.
Meanwhile, in a small bowl, combine the bread crumbs, parsley (if using), oil, 1 teaspoon of the salt, and the pepper; set aside.
In a saucepan, over medium heat, melt the butter. Stirring constantly, add the flour and cook for 3 minutes; the mixture will clump together. Still stirring constantly, add the milk slowly. Cook for 7 minutes. Add the Cheddar and the remaining salt and cook, stirring, until thick and creamy, about 5 minutes. Add the macaroni and combine.
Transfer to the baking dish and top with the bread crumb mixture. Bake until golden and bubbling slightly around the edges, about 25 minutes.