Combine the butter and sausage in a Dutch oven or heavy-gauge pot over high heat, and saute for about 6 minutes, stirring occasionally. Add the bell pepper, onion, celery, and garlic, and season with Creole seasoning, salt, and black pepper. Saute, still over high heat, for about 8 minutes, or until the natural sugars in the vegetables have browned and caramelized.
Add the tomatoes, shrimp, fish, and bay leaf, and stir. Add the rice, stir gently, and add the water. Gently move a spoon across the bottom of the pot, making sure that the rice is not sticking. Bring to a boil, then reduce the heat, cover, and simmer for about 15 minutes or until the rice has absorbed most of the liquid. Turn off the heat, then fold in the oysters, cover, and let sit for about 8 minutes, during which time the jambalaya will continue cooking from residual heat.
To serve, transfer to a serving bowl, and mix in the green onions. Season with hot sauce.
Thoroughly combine all ingredients in a blender, food processor, or mixing bowl, and pour the mixture into a large glass or plastic jar. Seal it so that it's airtight. It will keep indefinitely.
Recipe courtesy Ti Martin and Jamie Shannon, From Commander's Kitchen, Broadway Books 2000.