How to fix too salty macaroni and cheese?

I make my own and make the sauce from scratch. I made an oopsie with the salt today and it's too salty now. It's already all cooked, I figured out my error after dishing up.

I have now added extra cheese and milk but if I add any more it's going to be too liquify (for leftovers tomorrow)

What can I add to it to absorb the salt? I read something about a potato? Do I just cut it up and leave it in the dish overnight?