Sprinkle the pork with turmeric, salt and sugar and set aside.
Add all the spice paste ingredients to a dry frying pan over a moderate heat. Stir a little until the spices begin to pop and jump around the pan. Stir for no more than 30 seconds to avoid them burning - this will make curry bitter. Remove from the heat and quickly pour the spices into a spice grinder or pestle & mortar.
Grind the spices into a fine powder then pour in around 1 cup water. It'll be quite wet. Set aside while you complete the other steps and it'll thicken up.
In a food processor or using a hand blender, blend the onion, garlic and ginger into a puree.
Heat a wok or large pan with the oil over a moderate/high heat. When hot, drop in the curry leaves and let them splutter for a few seconds, before adding the onion paste. Stir fry this paste for about 5-7 minutes until browned and most of the moisture has evaporated.
Add the tomato and again, stir for 5 minutes until it's beginning to break down. Be careful no to let the paste burn.
Add the spice paste, and stir for about 30 seconds before adding the pork and 1 cup water. Stir well to combine everything. Bring to a boil, then reduce the heat to low. Pop on a lid and cook for 1½-2 hours until the pork is tender (you may need to adjust this time if you're using a different meat as they may take longer). The curry should be very gently bubbling.Stir every 15 minutes or so to ensure things are not sticking.
Once cooked, check for salt levels and adjust if you think it needs more. That's it!
Serve with Indian breads or lots and lots of fluffy basmati rice.