Parmesan cheese is not truly vegetarian, as it contains animal rennet. To make this dish 100% vegetarian, omit the cheese or find a suitable vegetarian substitute made without animal rennet. In supermarkets look for the 'parmesan style hard cheeses' which are suitable for vegetarians.
This is the best cheese sauce I've ever made - using cream really makes a difference to the texture and flavour, really nice! - 13 Sep 2012 (Review from Allrecipes AU | NZ)