Yep, it's hard for the European mind to accept that much cheese in a sauce, I suspect we aren't the only two Eurowankers to have made that mistake. The citrate is to emulsify the water and fats in the sauce so they stay mixed together, quite useful also for European-style sauces. All recipes agree on half of the cheese, at least, being cheddar, there's variation on the rest. In my case the mozzarella is there for texture, each of the others added its own touch to the flavour, that I found rich and balanced. Parmesan sounded also great, and not really pricier than the others over here, but it would've been too many and I had to choose. I used Italian pasta, radiatori specifically (this was the first time I bought them, literal wee pasta radiators lol) which held the sauce very well, it's gonna be in the oven for a bit so don't overcook it or it'll end up soft.