2) Add the onion, green pepper, celery and garlic and cook over low heat for about 5 minutes, until the vegetables are limp. Add the black pepper, white pepper, cayenne pepper, Cajun seasoning, spring onions, parsley and hot sauce to taste.
3) Add one can of clam juice and the tomatoes with their juice, stirring to blend. Add the salt, starting with 1 teaspoon and adding more if needed. Bring the mixture to a boil, reduce the heat to low and simmer for 10 to 15 minutes.
3) Add the prawns and stir. It will take about 3 minutes for the prawns to cook, don't overcook. Remove the saucepan from the heat. Add the butter and stir; the heat from the dish will melt the butter.
4) Transfer the etouffee to a terrine dish, serving bowl or, if you prefer, serve over rice. Garnish with spring onions.
Cook's note: To make a roux use oil instead of butter, because butter burns easily.