This version of pasta and beans is more a thick stew than a soup. If you prefer it thinner, add more stock or broth, or even water. If desired, add a Parmesan rind along with the stock.
Heat in a large saucepan over medium heat:
Add and cook, stirring, until the onion is golden brown, about 8 minutes:
Stir in:
Cook for 1 minute, then add:
Partially mash the beans with the back of a spoon. Add:
Bring to a simmer, partially cover, reduce the heat, and simmer for 5 minutes. Stir in:
Cook until the pasta is tender. Thin the sauce, if needed, with additional stock, broth, or water. Season to taste with:
Just before serving, stir in:
Ladle into bowls and serve with additional grated cheese.