Melt butter in large pot over medium heat; whisk in flour and cook 2 minutes until toasty.

Gradually whisk in milk until smooth; bring to gentle simmer.

Stir in dry macaroni; cook on medium-low 8-10 minutes, stirring often, until pasta is tender and sauce thickened.

Remove from heat; add cheddar in two batches, stirring until melted and smooth; season with salt and pepper.

Rest 2 minutes to thicken, then serve.