Peel and chop the onions. Warm the goose fat in a casserole over a moderate heat, add the onions, chopped carrot and celery and cook until soft and pale gold. Cut the bacon into small pieces, cooking it until the fat is gold, then pour in the stock and add the thyme, bay and rosemary. Submerge the bones, add any meat juices or jelly, the peppercorns and a piece of parmesan rind if you have it, then bring to the boil. Lower the heat to gentle simmer for 45-60 minutes.
Crush the garlic to a paste with a pinch of sea salt then mash in the basil leaves, pine nuts and olive oil, then the parmesan.
Add the beans to the soup and continue cooking for a further 10 minutes. At this point you can skim off the fat if you wish, but I don’t – instead, relishing the silkiness it lends to the soup. Ladle into bowls and stir in the basil sauce.
