how much cornstarch? is it necessary or can i just add more cheese?

I can't imagine putting cornstarch into a pasta sauce, so I'd just leave it out. I probably wouldn't add more cheese, but I would serve additional cheese at the table so anyone who wants more can add it to their taste.

For anyone else who might have been wondering, here is MaggieRosenthal's response from the recipe comments -- "Hi Igor, thanks for catching the left out ingredient! I'd say about a tablespoon of cornstarch, maybe less -- it's to help the cream sauce thicken up a bit, so you can put half a tablespoon in, whisk, see if you like the consistency, and add more if you want it to be thicker. It's not necessary to have cornstarch if you don't want it because it's not there for any flavor benefits, it's more about preference in terms of the sauce's thickness."