In Tuscany we make these Crostones in winter when the Cavolo Nero is young. It's a way of using up stale bread and when Cavolo Nero grows in such quantities you don't know what to do with them. They do a great vegetarian first course or just a light dinner in itself. In the US you would use Black Cabbage or Tuscan Kale as I have found out on the internet. —Maria Teresa Jorge
Wash the dry cannellini or borlotti beans and soak them in water overnight.
In a large pot add the soaked beans, cover with water, add 2 tablespoons of olive oil, the sage leaves and 1 garlic clove. Do not cook them with salt or they will remain hard. Cover the pot with a lid and simmer about 20 minutes or until they are cooked. Add salt to taste and simmer for another 10 minutes uncovered.
Choose the younger leaves of your cavolo nero and wash them. Roughly tear them up and sautee them in 2 tablespoons of olive oil until al dente.
Cut the bread in slices 1/2 inch thick and when you have the Cavolo Nero and beans ready, put the bread slices under the grill and lightly toast them.
Have all the ingredients next to you so you make the crostone really quickly and serve them straight away otherwise they will become horribly soggy.
Cut the other garlic in half and very very lightly rub the toasted bread with the cut surface of the garlic clove. Top with the some sauteed cavolo nero and add on top some cooked beans. Drizzle a little extra virgin olive oil, a pinch of freshly ground black pepper and sprinkle with some fleur de sel.