Saute onion, carrot and celery with a little salt on a gentle heat for about ten minutes in a large saucepan. Sometimes I add a little crushed garlic or if I have no celery I will use leeks. Stir occasionally.
Add tomatoes (you can use fresh skinned tomatoes or tinned ones with their juice) and cook for a further ten minutes stirring occasionally.
Add cooked borlotti beans and bean cooking liquid topped up with stock (I use Marigold Bouillon powder with water). I usually make sure there's at least two inches of liquid above the beans and vegetables in the pan.
You can add fresh uncooked borlotti beans instead at this point if you have them (about 1kg in weight in their pods - then shell and discard pods and compost them). Or add some tinned beans like red kidneys.
Simmer for half an hour with the lid on.
Taste and season with salt and pepper if necessary - you can also take out a few of the beans (a couple of tablespoons and mash them and add back into the pan)
At this point you can add a couple or three handfuls of dried small pasta shapes like orzo or macaroni and cook for a further 10 or 15 minutes making sure there's enough liquid to absorb the extra ingredients.
I usually don't bother.
I chop lots of fresh parsley - a couple of tablespoons and add five minutes before I serve.