In a medium-sized saucepan melt better and cook over medium heat, making sure it does not turn brown. Stir in flour; cook for 2 minutes.
In a separate saucepan, add milk and bring to a simmer, making sure not to scorch the bottom of the pan. Whisk warm milk into butter/flour mixture. Whisk in cheese, then season the sauce with salt and pepper.
Cook pasta according to package directions, then drain and toss with the sauce. Fold in cilantro.
