This is a cross between a pasta dish and a soup, depends on how much liquid you add. I use canned beans for convenience. (You may use dried, just soak them overnight and make sure you cook them for a long time in the sauce).
This is basically the way my mother-in-law made it, with my twist (which is a different twist every time I make it!)
1 onion, chopped
1-2 sticks of celery, chopped
1 can of tomatoes (crushed or whole and puréed)
Salt and pepper to taste
Fresh parsley, chopped
1 can cannellini beans (or more, if you wish), drained
1 lb small pasta, tubetti, ditalini, elbows
Sauté the chopped onion in the olive oil, till it’s well cooked, starting to turn golden. Add the celery, cook a few more minutes. Add the tomatoes, salt and pepper, parsley and simmer about 15 minutes. Add the drained beans, a little water, cover and cook at least 30 minutes more – the beans must be very soft. Add more water as needed to keep it a bit soupy.
Cook the pasta very al dente. Drain it, then add it to the pot with the sauce, mix well, add some of the pasta water to keep it on the soupy side.
Serve with grated parmigiano, grana or pecorino (this is very personal, some people don’t like to add cheese. I think it’s a great addition.)