First, clarify the butter. Melt the butter in a heavy saucepan over low heat. Let it simmer until the foam rises to the top. Once the butter stops making crackling noises and there is no longer any foam rising to the top, remove from the heat and let it cool slightly. Most of the solids will be on the bottom. Skim off any foam with a spoon. Strain through a cheesecloth-lined strainer.
After clarifying the butter, you will have about 4 to 5 tablespoons for the roux.
Chop the onions, celery, bell pepper, and garlic. Set aside.
Put the clarified butter in a Dutch oven or large heavy saucepan. Heat over medium-low heat and add the flour.
Cook, whisking constantly, until the roux is golden brown, about the color of peanut butter.
Add the chopped vegetables to the roux and continue cooking, stirring frequently, until the onions are translucent, about 10 to 12 minutes.
Add the clam juice or shrimp stock and tomatoes, along with 1 tablespoon of the Creole seasoning, bay leaf, and ground black pepper. Bring to a boil. Reduce heat to low and simmer for 30 to 45 minutes or until the vegetables are softened.
If the sauce mixture seems too thick, thin it with a little more clam juice, shrimp stock, or some chicken broth.
Taste and add more Creole seasoning and salt, as needed.
Add the shrimp and continue cooking for about 3 to 4 minutes or until the shrimp are cooked through.
For each serving, put a big scoop of rice in the center of a deep plate or shallow bowl. Spoon the shrimp étouffée around the rice. Sprinkle with a little fresh chopped parsley or green onion tops. Serve with a simple tossed salad and crusty French bread or rolls.