1. Begin the soup 2 days in advance. Rinse the kale and other greens and strip away the hard stems. Sprinkle the leaves generously with salt and drain in a colander in the sink for 30 minutes. Rinse and squeeze dry; then coarsely chop them.

2. Meanwhile, heat half the olive oil in the 5-quart casserole over medium heat. If using earthenware, be sure to start on low and raise the heat gradually. Add the chopped yellow onions, celery, and carrot and cook until the vegetables are soft and just turning golden, about 20 minutes. Add the greens to the pot, stirring to coat them with oil.

3. Crush half the cannellini beans to a puree. Add all the beans, the garlic, parsley, thyme, bay leaf, tomato sauce, and cheese rind to the mixture and cook, stirring, for a few minutes. Pour in 3 quarts warm water and slowly bring to a boil. Cover, reduce the heat, and simmer for 30 minutes to blend the flavors. Remove from the heat, uncover, and let cool.

4. Stir the bread into the cool soup and return the pot to low heat. Raise the heat to medium-low and cook, stirring, until the bread crumbles and the soup turns creamy with small bread chunks here and there. Add water if necessary to keep the mixture smooth but always so thick a spoon can stand up in it. Let cool, cover, and refrigerate for 2 days.

5. About 3 hours before serving, remove the soup from the refrigerator. Correct the seasoning with salt, plenty of black pepper, and a splash of vinegar. Remove the cheese rind (see Notes). Preheat the oven to 350°F.

6. Lightly oil the 12-inch-wide casserole and turn the ribollita into it. Top with slightly overlapping slices of red onion. Drizzle the remaining 1/3 cup olive oil over the top and bake for 2 hours. Turn off the heat and leave the dish in the oven until it cools down to warm, 35 minutes. Serve with a pepper mill and a cruet of your best Tuscan extra virgin olive oil.