Blend together paste ingredients (spring onion, turmeric, lemongrass, garlic, ginger & chilli) in a food processor or blender.
Heat oil, add spice paste and dry spices. Fry til fragrant.
Add beef and stir to coat.
Add tamarind, lime juice and coconut milk. Bring to a boil, then lower to a gentle simmer for 1 hour. Put a lid on the saucepan for the first 30 minutes. If the gravy dries out, add extra water to keep it moist, but not soupy.
Add lime zest, brown sugar and toasted coconut.
Continue to simmer until meat is tender and the gravy as reduced to a coating on the meat rather than a liquid sauce (another 1-2 hours), but keep an eye on it so that it doesn’t completely dry out and burn.
Notes
As with all curries, this is best made the day before.