In a large saucepan of boiling, salted water, cook the macaroni until al dente; drain in a colander.
In the same saucepan, melt the butter over medium heat. Whisk in the flour and cook for 1 minute. Gradually whisk in the warmed half-and-half and cook, whisking constantly, until the mixture is steaming hot and thick, about 4 minutes. Remove from the heat and stir in the cheddar until melted. Stir in the cooked macaroni and season to taste with salt.