Have all ingredients ready before you start cooking.
Make the roux. In a heavy pot, melt the butter over medium heat. Add the flour and stir to combine. Lower the heat and continue to stir constantly until roux becomes a brown color. This should take about 20 minutes. Do not walk away while cooking at any time. Should the roux burn, start over for it is unusable.
Once the roux is finished, add to the pot the chopped onion and bell pepper. Stirring continuously, cook about 5 minutes until soft. Add the garlic and the 1 tablespoon tomato paste. Stir to combine.
Add the basil, thyme, ground peppers and Creole seasoning. To the mixture add 3 cups water and stir. Simmer on low for about 10 minutes, stirring (from the bottom of the pot) frequently. Adjust seasoning with salt and pepper, if necessary.
Stir in the green onions and crawfish tails; heat through on low heat, about 10 minutes. Add additional water, if necessary.
Serve with hot cooked rice and garnish with chopped parsley.