[Chinese] How to cook Homemade Sichuan-style lamb shanks

Ingredients
- 60 ml (¼ cup) vegetable oil
- 4 lamb shanks
- 2 celery stalks, 1 halved lengthwise, 1 thinly sliced
- 2 long red chillies, 1 halved lengthwise, 1 thinly sliced
- 2 leeks, 1 quartered, 1 thinly sliced
- 75 g (â…“ cup) black bean and garlic sauce
- 2 tsp ground cumin
- 1 L beef stock
- 1 tsp Sichuan peppercorns
- chopped flat-leaf parsley, to serve