Would foie gras and swiss be worse?
Like the cheeseburger that Lazmataz proffered, it would be a mixture of things considered kosher under Jewish dietary law, in and of themselves, but considered tref, or unclean, when served combined (Jewish dietary law prohibits the mixing of meat and dairy products in the same dish.)
Ham, on the other hand, is always considered tref, as it is derived from pork, which is always unclean under Jewish dietary law.
the infowarrior