Bring a pan of water to boil and season heavily with salt. Add pasta and stir. Make sauce while pasta cooks.
Melt butter in a wide skillet. Once it's melted, whisk in flour and cook 30 seconds until golden.
Add milk and whisk again until smooth, then add cheese in batches, stirring constantly until all the cheese is incorporated.
Add seasonings, including the salted pasta water to both season and loosen.
When pasta is ready, transfer to skillet with either a slotted spoon or a wire spider, and do not drain first. Whatever water is still in the pasta will also come along and help smooth out the sauce and achieve desired consistency. Thin with additional pasta water if necessary.