Add the oil to a large pan over a moderate/high heat. When hot, add in quick succession the curry leaves, fenugreek seeds, cumin seeds, cardamom pods, fennel seeds, black peppercorns and finally the onion. Turn heat down to medium and stir well. Fry gently for 4-5 minutes until the onion is soft.
Add the fenugreek leaves and fry again for 1-2 minutes before adding the mushrooms.
Stir well Stir fry the mushrooms for about 3 minutes until they've softened slightly. Add the tomatoes, chilli powder, paprika, turmeric, garam masala, cumin, coriander and salt. Stir well for 1-2 minutes then add 1½ cups water followed by ¾ cup of coconut milk.Bring to a simmer then reduce heat to medium/low. Place lid on pan and simmer gently for 10 minutes.
Remove the lid from the pan and simmer uncovered to reduce the sauce for 5-10 minutes. It should be creamy! Sprinkle over the dried fenugreek leaves and drizzle over the ¼ cup of coconut milk. Stir one last time then remove from the heat and serve!