Whisk together the yoghurt, ground turmeric, chilly powder, salt and ginger paste in a bowl and marinate the mutton in this mixture for 3-4 hours or overnight in the fridge.
Heat a pan on low heat, add the coriander powder and dry roast for 20 - 30 seconds. Put it aside in a bowl.
Pour oil into the same pan and toss in the sliced onions. Fry on a gentle heat till translucent with golden edges. Then add the garlic, pounded spices, poppy seeds and half the curry leaves and sauté for a minute.
Tip in the marinated mutton and fry for a couple of minutes. Then put a lid on the pan, lower the flame to minimum and cook till the mutton is tender. While the mutton cooks, stir intermittently, scraping the browned masala sticking to the pan and adding a little water as needed. Do this till the meat is cooked.
Once the meat is cooked, check and correct the salt, add the remaining curry leaves and ground pepper, increase the flame to medium and fry till the gravy thickens up and the meat is a rich, dark brown. Turn off the heat and serve.