The Zolfino bean from Pratomagno
Slow Food Ark of Taste variety which means that it is endangered.

It was Emperor Charles V who supposedly introduced beans to Tuscany, following the European discovery of the New World, gifting them to Pope Clement VII (Giulio de’ Medici). As well as the more common Cannellini and Toscanelli, other rarer varieties are still grown here, like Coco Nano and the excellent Zolfino.
Also known as the Fagiolo del Cento, the “bean of the hundred” (because they were traditionally sown on the 100th day of the year), or Burrino, the Zolfino bean is small, spherical and yellow, with a pale eye. They have long been cultivated between the Arno River and the Pratomagno mountains, in the province of Arezzo, at altitudes of 250 or 300 meters above sea level, or even as high as 600 meters. They love poor soil and cannot survive in lower-lying areas, because their very shallow root system cannot tolerate the slightest amount of waterlogging. The beans are usually sown in April, often on terraced land under olive trees, so that any water drains away between the stones of the drystone walls.
Despite their thin skin, Zolfino beans can stand long cooking times (three or four hours or more). When cooked, they are dense and creamy, melting in the mouth like butter. They are usually served boiled and dressed with a drizzle of intensely flavored, fruity extra-virgin olive oil over grilled slices of Tuscan bread, or as an accompaniment to Fiorentina steaks.
Traditionally—and still today in some places—they are cooked overnight in a flask or earthenware pot placed in a wood-burning oven after the bread has been baked. The leftovers make the perfect addition to ribollita.