Prawns in Coconut Milk

This is an Indian curry I was served by a Bengali friend in Bangladesh. It's a delicious curry and not very difficult to make.

1 1/2 lbs (750 g) large raw prawns
1 tablespoon ghee (butter) or oil
2 medium onions, thinly sliced
2 cloves garlic, crushed
1 tablespoon finely grated fresh ginger
2 fresh red or green chilies, clit and seeded (optional)
1 teaspoon ground turmeric
8 curry leaves
2 cups coconut milk
1 tsp salt
Lemon juice to taste

Wash prawns well. Shell and devein if liked, but some local cooks say the prawn should be in their shells, for they retain more flavor this way. (I would recommend shelling and deveining).
Heat ghee (butter/oil) and fry the oions, garlic and ginger until onions are soft but don't let them brown. Add chillies, turmeric and curry leaves and fry 1 minute longer. Add coconut milk and salt and stir while bringing to simmering point. Simmer uncovered for 10 minutes, then add prawns and cook for 10-15 minutes. Remove from heat and add lemon juice to taste.