I made the pot de crème recipe from the sous vide beyond the basics class, recently... and used Kilner jars as in the recipe. The results were fantastic, so I'd recommend giving it a go! However, I'm wondering if I could I make them again, but instead use eg. ramekins wrapped in clingfilm? I don't see why not, but I don't want to make a batch and it go catastrophically wrong! Obviously air couldn't escape, but it could expand and the clingfilm would 'just' bulge up, right?