Cook the macaroni according to the package directions.
Meanwhile, heat 1 tablespoon of the butter in a large saucepan over medium heat. Add the bread crumbs and cook, stirring, until golden, 1 to 2 minutes. Stir in 1/4 teaspoon salt, 1/4 teaspoon pepper, and the parsley (if using). Transfer to a small bowl and set aside.
Wipe out the saucepan and melt the remaining tablespoon of butter over medium heat. Add the flour and cook, stirring, for 2 minutes. Whisk in the milk and cook, stirring occasionally, until the sauce has slightly thickened, 5 to 7 minutes. Add the Cheddar and 1 1/2 teaspoon salt and whisk until the cheese melts. Stir in the macaroni.
Divide among bowls and sprinkle with the bread crumbs.