Prepare the Vegetables: Finely dice the onion, green bell pepper, and celery. Mince the garlic.
Make the Roux: In a large, heavy-bottomed pot or Dutch oven, melt the butter over medium heat. Add the flour and cook, stirring constantly, until the roux is a light golden-brown color, about 5-6 minutes.
Sauté the Vegetables: Add the diced onion, bell pepper, celery, and minced garlic to the roux. Cook, stirring frequently, until the vegetables are softened, about 6-8 minutes.
Build the Sauce: Gradually add the broth, stirring constantly to prevent lumps. Add the Worcestershire sauce, hot sauce, Cajun seasoning, paprika, cayenne pepper, and bay leaf. Bring the mixture to a simmer and cook for 8-10 minutes, until slightly thickened.
Add the Crawfish: Stir in the crawfish tails and green onions. Simmer for an additional 5-7 minutes, allowing the flavors to meld together. Taste and adjust seasonings with salt and black pepper as needed.
Serve: Remove the bay leaf. Serve the Crawfish Étouffée over a bed of fluffy white rice. Garnish with fresh chopped parsley.