For the Sri Lankan curry powder, simply grind everything together in a spice grinder into a fine powder. Store in a screw top jar.
Rinse the fish steaks under cold water and dry on kitchen paper. Heat the oil in a large, shallow pan, add the onion, garlic, curry leaves and 'rampe' if using and fry gently for 7-10 minutes until the onions are soft and lightly golden.
Add the turmeric, chilli powder and 2 tbsp of the Sri Lankan curry powder and fry for 1-2 minutes. Add the tomatoes, tamarind liquid, coconut milk and 1 tsp of salt and simmer gently for 15 minutes.
Add the salmon steaks to the pan and spoon some of the sauce over the top of the fish. Simmer gently for 5 minutes, then cover the pan and set aside for 30 minutes. By this time the fish should be cooked through - but if not, just return to the heat for a few more minutes until it is. Serve with some steamed basmati rice.