Nigel Slater's classic ribollita.

Nigel Slater's classic ribollita | Life and style | The Guardian
Ribollita - which means 'boiled twice'.
Literally "re-boiled", this sustaining, ancient recipe is the very essence of kitchen economy – a big fat soup substantial enough to be a main course.

THE RECIPE
Leave 2 peeled onions,
2 carrots,
3 peeled cloves of garlic and
3 ribs of celery, all roughly chopped, to cook for 20 minutes in a couple of tbsp of olive oil in a deep pan.
When they are soft, stir in a 400g can of chopped tomatoes, and
250g cooked cannellini beans with
250ml of their cooking water and a couple of bay leaves.
Leave to simmer over a low to moderate heat for 30 minutes.
Tear up 4 thick slices of bread and dunk them into the soup.
Chop four large handfuls of cavolo nero or other kale and stir it in.
Season and continue to simmer for 15-20 minutes until you have a thickish soup, adding more bean water if you need to.
Serve in bowls with a trickle of olive oil on each.

THE TRICK
A night in the fridge will encourage the flavours to marry.
Keep the pieces of vegetable quite small – the soup should be thick, but not a chunky stew.
Use a firm white loaf, torn into rough chunks.

THE TWIST
Cavolo nero is pretty much a given if you are adding greens to your ribollita, but spring greens and Savoy cabbage also make fine alternatives to the finished soup.
Some cooks add cubed potatoes, courgettes, diced prosciutto, leeks, thyme leaves, fennel seeds and crushed dried chillies.
I like to pour in a spoon of lemon oil too at the last minute to brighten up the flavours.

Note: Substitute for Cannellini Beans (large white Italian kidney beans ): - Great Northern or white (navy) beans or flageolets.