Boil the bamboo shoot in plenty of water for 20 mins till tender, drain and chop into large chunks.
To make the spice paste, dry roast the coriander, cumin and fenugreek seeds in a pan till they're fragrant (30-40) seconds. Take care not to burn them. Cool and grind to a thick paste with the coconut and peppercorns.
Heat ½ tablespoon of coconut oil in a heavy bottomed pan or kadai and lsear the mutton in batches till they're light brown on the edges. Set aside.
Add the remaining oil to the pan and crackle the mustard seeds and half the curry leaves. Add the onions and sauté on a low flame till they're translucent.
Now put in the garlic and ginger and cook for 20 seconds more. Add the coconut paste and turmeric powder and gently fry the masala for another 20 seconds taking care not to burn it. Sprinkle a little water if required.
Tip in the mutton and the bamboo shoot and mix well to coat the pieces with the masala.
Add 300 ml water, chilli powder, green chillies, the remaining curry leaves and salt. Bring the curry to a boil. Lower the heat, cover the pan and simmer the curry for 30-40 minutes or till the meat is cooked and falling off the bone. The meat will give off some liquid, so add more water only if required.