I'd like to report that the
truly official website for Leonardo's Last Supper is
https://musei.lombardia.beniculturali.it/musei/museo-del-cenacolo-vinciano/i.e. the dedicated page in the Lombard section of the site of the ministry for cultural heritage and tourism. It sketches all details, even if only the Italian version has a working link to VIVATICKET (why?!).
The one provided now (http://legraziemilano.it/) has its link to the Last Supper dead at the moment, but besides that, it does not belong to those who manage the Last Supper's museum*. The church and the museum are two completely separate entities.
I hope this information will help some future visitor, because unfortunately the web brims with
para-sites which have all the look of officiality but offer overpriced, guided tours and give a misleading impression of the visit. I don't understand why they rank so high in search engines with respect to the official one.
*Absurd note: if you go look at the section
Omelie domenicali ('Sunday sermons'), you will find the
Lorem ipsum. Well, this gives a measure of how well the site is maintained...
Dio santo (= my God).