Boil the Pasta:
Bring a large pot of salted water to a boil. Cook elbow macaroni until al dente, about 6–7 minutes. Drain and set aside.
Make the Cheese Sauce:
In a medium saucepan, melt butter over medium heat. Whisk in flour and cook for 1–2 minutes. Slowly whisk in warm milk. Cook until thickened, then stir in cheddar cheese, salt, and pepper until melted and smooth.
Combine:
Preheat oven to 350°F (175°C). Mix cheese sauce with cooked pasta in a large bowl. Stir to coat evenly.
Bake:
Transfer mixture to a greased 2-quart baking dish. Top with extra cheese or breadcrumbs if desired. Bake uncovered for 25–30 minutes, until bubbly and lightly golden.
Rest & Serve:
Let rest for 5–10 minutes before serving. Enjoy warm with a side salad or roasted vegetables.