Melt butter in a medium saucepan over medium heat.
Add flour, stirring until combined. Cook, stirring frequently, for 5 minutes, or until golden (do not let brown).
Add milk to butter mixture, whisking until completely smooth and no lumps remain.
Simmer mixture, stirring frequently, until sauce coats the back of a spoon, 5 to 8 minutes.
Add cheese to saucepan in batches, stirring until completely melted. Add salt and pepper, stirring to combine.
Place cooked macaroni in a large bowl. Add cheese sauce, stirring to combine. Serve immediately.
