Parmesan Reggiano or at worst Gran Padano
No cashew nuts. No sunflower oil. No hydrogenated anything. No potato.
There are more sinners against pesto than I care to mention. I'm not criticising rocket pesto or walnut pest or coriander pesto or anything else that confesses on the label that it's not the real thing; I'm dissing what Sacla produces for the UK and what comes in most jars. Sainsburys has done well for several years; the fresh green pesto they do is really pretty good, with few extraneous icky things. Waitrose didn't do a pesto worth the name till last year, but now they have a superb pesto - bright green with extra whole pine nuts in. Sainsburys has something similar but more expensive and in a pot you can't reseal - truly delicious though. The Jamie Oliver pesto in a jar and the own-brand Waitrose in a jar were both true to the recipe the last time I checked, though not a patch on fresh. The deli in Putney still does superb pesto too ;-)
And while I'm on food, a 'too good to live' nomination for lamentables for greeting worn out M40 travellers with not just a welcome cuppa but a delicious chili - thank you again!