As I am of the opinion that Vermont Butter and Cheese Company, produces the best butter in this country (their Cultured Butter), it seems odd that I would be recommending an Italian butter. Odd until it is noted that Delitia butter shown in the above photo can be purchased locally.
Delitia is an importer of Italian, high quality food products and their butter seems to be the only one of their products that I find on a semi regular basis here in the Bay Area. It has a very distinctive, only very slightly "Parmigiano" taste, very high in butterfat. It takes a concerted effort to find that nutty taste, but it's there, and that is why I like this butter as much as I do.
I buy it whenever I can find it and sometimes freeze it. It can most often be found at Bryans in Laurel Village and Milk Pail. Costco imported a different brand of butter from the same area and it was excellent as well, but seemed milder in flavor.