Cut off the roots of the lemongrass. Measure about an inch from the root end, use this and discard the rest. Slice thinly the part that you’re using.
Peel the onions and roughly chop.
Cut the chilis into small pieces.
Place the chopped onions, lemongrass and chilis in the blender, pour in the oil and process until smooth.
Pour the paste into a frying pan. Cook over medium heat until the semi solids start to separate from the oil.
Mix together the coconut milk, turmeric and tamarind paste. Pour the mixture slowly into the frying pan. Season with fish sauce. Add the fish and simmer until the fish is cooked through.
Pour in the coconut cream, stir until the gravy thickens a bit then transfer to a serving bowl or platter and serve at once.