Tuscan countryside — a quintessential contadino dish from the Casentino valley, the Chianti hills, and the Mugello. The name refers to the practice of reheating the soup over several days — refrigeration-era cooking in a pre-refrigeration tradition.
Ribollita — 'reboiled' — is the iconic Tuscan cucina povera of bean-and-bread soup cooked once, cooled, then reheated (reboiled) the next day until it thickens to a mass that holds its shape on a ladle. At that stage it is sometimes fried in a thin layer in a pan with olive oil, browning the underside like a savory bread cake. The defining vegetables are cavolo nero (Tuscan black kale), cannellini beans, and stale bread — and the flavour depends entirely on the quality of all three.
Day-one ribollita is merely very good bean-and-vegetable soup. Day-two ribollita — thick, dark from the cavolo nero, starchy from the bread, with the pepper-and-grass of Tuscan olive oil — is a completely different experience. The oil is the finishing condiment and flavour anchor; a great Tuscan oil transforms the dish.
Day one: a substantial minestrone-style soup with cannellini beans (cooked from dried — never tinned for ribollita), cavolo nero, lacinato kale or savoy cabbage, onion, carrot, celery, tomato, and stale unsalted Tuscan bread (pane sciocco) torn in. The bread absorbs liquid overnight and thickens the soup. Day two: reheat gently, stirring as it thickens — it should become almost porridge-like. Pour into bowls, finish with the best Tuscan extra-virgin olive oil you have. The Tuscan oil — bitter, grassy, peppery — is the defining final flavour. Without good oil, ribollita is just thick bean soup.
The fried version ('ribollita fritta') is made by spreading the cold, thick day-two ribollita into an oiled pan and frying until a crust forms on the bottom — then either served inverted or scooped. The crust is one of the great textures in Tuscan cooking. The ribollita improves with each reheating — day three is often better than day two.
Using tinned beans — lack of body and flavour from the bean cooking liquid, which is part of the soup base. Using ordinary salted bread — the unsalted pane sciocco is traditional and necessary; salted bread skews the seasoning. Serving day one — ribollita requires the overnight rest for the starch in the bread to fully absorb and the soup to thicken. Not finishing with olive oil — this is the most common error; the oil is not optional.
Marcella Hazan, Marcella's Italian Kitchen; Faith Willinger, Eating in Italy