1.Preheat oven to 220ºC.
2.Roast ham hock and onion in a medium baking dish for 30 minutes.
3.Place hock and onion in a large saucepan with coarsely chopped celery, peppercorns, bay leaf and the water; bring to the boil. Reduce heat; simmer, uncovered, 2 hours.
4.Remove hock from broth. Strain broth through a muslin-lined sieve or colander into a large heatproof bowl; discard solids. Allow broth to cool. Cover; refrigerate until cold
5.Remove ham from hock; shred coarsely. Discard bone, fat and skin.
6.Meanwhile, heat oil in cleaned saucepan over medium heat. Stir carrot and extra celery over heat for 2 minutes. Add ham, garlic, paste and tomato; continue stirring 2 minutes
7.Discard fat from surface of broth. Pour broth into a large measuring jug; add enough water to make 2 litres (8 cups). Add broth to pan and bring to the boil. Reduce heat and simmer, covered, 20 minutes.
8.Add leek, pasta and beans to pan; bring to the boil. Reduce heat; simmer, uncovered, until pasta is tender. Remove from heat and stir in herbs. Season to taste.
9.Serve soup topped with parmesan.