Sauté garlic and leeks in olive oil for three minutes.
Add carrots, celery and meat.
Cook for about 10 minutes then add beans and half the parsley.
Toss to coat and pour in stock, tomatoes and sugar, and season to taste.
Bring to the boil, reduce heat and simmer very gently for one to one and a half hours.
Stir in the tomato paste and simmer for a further 30 minutes, until thick and velvety.
Season well and toss in the remaining parsley.
Note: You could use a ham hock in place of the lamb knuckle, just replace the lamb stock with chicken stock.