Heat a large pot of salted water to a boil, drop in pasta. Cook pasta to just shy of al dente.
Heat sauce pot with butter over medium heat, whisk in flour and cook for 1 minute, whisk in stock then milk, allow the sauce to thicken, and season with salt, pepper and nutmeg. Stir in cheeses in a figure eight motion. Stir in Dijon and ham and remove the sauce from heat. Drain pasta and combine with sauce.