Spoon about 1/3 cup of the thick coconut cream from the top of the coconut milk and in a large heavy skillet cook the cream over moderate heat, stirring, for 2 to 3 minutes, or until it is thickened slightly.
Add the curry paste and cook the mixture, whisking, for 1 minute.
Add the shrimp and sauté the mixture over moderately high heat, stirring, for 1 to 2 minutes, or until the shrimp turn pink.
Add the coconut milk and the naam pla and simmer the mixture, uncovered, stirring occasionally, for 1 minute, or until the shrimp are just cooked through.
Transfer the shrimp with a slotted spoon to a bowl, to the skillet add the carrots and the bell pepper, and simmer the mixture for 5 minutes.
Add the spinach in batches, stirring until each batch is wilted, return the shrimp to the skillet, and simmer the mixture, stirring occasionally, for 1 minute.
Sprinkle the dish with the coriander and serve it with the rice.