Peel the shrimp, reserving the heads and shells. Refrigerate the shrimp until ready to use. In a saucepan, over medium heat, combine the reserved heads and shells, onions, lemons, bay leaf and water. Season with salt. Bring the liquid to a boil. Reduce the heat to medium-low and simmer for 30 minutes. Strain and set aside. Season the shrimp with salt. Toss the shrimp with the curry paste. In a saucepan, over medium heat, add the oil. When the oil is hot, add the onions. Season with salt. Saute for 2 minutes. Add the peppers, garlic and seasoned shrimp. Saute for 2 minutes. Add the reserved shrimp stock. Bring the liquid to a boil. Reduce the heat to medium-low and simmer for 5 minutes. Stir in the coconut milk. Adjust the seasonings. Remove from the heat and stir in the basil. Ladle into serving bowls and serve.
Remove and discard the outer leaves and upper half of the lemon grass stalks, and chop the bottom half into 1-inch pieces. Soak all the dried ingredients for 30 minutes, or until softened. Place all the ingredients in a food processor, and blend to a smooth paste. Add a little water if necessary to thin.
Recipe adapted from Adriana's Spice Caravan: Storey Communications, Inc. 1997