1. Melt the butter over medium heat in a large heavy pot. Add the Creole seasoning, thyme, celery, bay leaves, onions and bell peppers and cook until the vegetables are soft, about 15 minutes. Add the tomato paste and cook, stirring, until well incorporated and beginning to caramelize, 2 minutes. Stir in the crawfish tails and cook until they release their liquid, 2 minutes. Sprinkle in the flour, stir until it is absorbed and cook until thickened, 1 minute. Slowly whisk in the fish stock, and then add the vinegar, Worcestershire and hot sauce. Bring to a simmer, reduce the heat to medium-low and cook until thickened and the flavors have developed, 15 minutes.
2. Just before serving, stir in the half of the parsley and half of the scallions and simmer 3 minutes more. Add the lemon juice and season with salt. Serve over hot cooked white rice garnished with the remaining parsley and scallions.
Using frozen crawfish tails makes this recipe fast and easy, but if you can get live crawfish, the flavor can't be beat. Cook the live crawfish in a large pot of boiling water for about 15 minutes, separate the tails and extract the meat. Use some of the boiling liquid in place of the fish stock or water.