I'm rather partial to beef tendons, but you won't find them in your local butcher's – they are more common in Asian supermarkets. If you can't get hold of them, then you can use flank or shin to make an equally tasty broth, but you won't quite get the same gelatinous texture as you do with tendons. Asian supermarkets often sell fresh green peppercorns, or you can use canned.
For the broth
400-500g beef tendons cut into 4-5cm chunks
2ltrs beef stock
6 cloves of garlic, peeled and crushed
60g root ginger, scraped and sliced
150ml rice wine
1 star anise
30-40 fresh green peppercorns
For the wontons
150g fatty minced beef
2 spring onions, finely chopped
20g root ginger, scraped and finely grated
Salt and freshly ground white pepper
12 wonton wrappers
150g bok choi or pak choi, cut into pieces
10 spring onions, shredded on the angle
A few sprigs of coriander
For the broth, put all of the ingredients except the green peppercorns into a saucepan, bring to the boil and simmer for about 2-2 hours very gently with the lid on, or until the tendons are soft and tender; top up with water if necessary. It's difficult to put a cooking time on tendons so they may well need longer. Add the peppercorns for the last 15-20 minutes of cooking.
Meanwhile, mix the minced beef with the spring onion and ginger; season. Lay the wonton wrappers on a work surface and spoon the mixture into the centre of each. Dampen the edges with cold water and gather the edges up over the filling and gently pinch the wonton together just at the top of the filling to seal it. To serve, remove the pieces of tendon from the broth, cut into bite sized chunks and return to the broth. Re-season the broth if necessary; top up with a little more water if it has reduced too much. Bring the broth back to a simmer and drop in the wontons, simmer for 3-4 minutes then add the pak choi and simmer for another couple of minutes. Transfer to a serving bowl or bowls; scatter the coriander over.