Measure and dice the onion, green pepper and celery (the holy trinity). Mince the garlic, chop the parsley and slice the scallions. If using frozen crawfish tails, thaw and drain them; pat dry with paper towels.

Make the roux

In a heavy-bottomed skillet or Dutch oven over medium heat, melt the butter. Add the flour and whisk constantly, cooking until the mixture reaches a light to medium brown color (about 6–8 minutes). Do not let it burn — stir and scrape the bottom frequently. The roux should smell nutty and be the color of peanut butter.

Cook the vegetables

Add the diced onion, green pepper and celery to the roux. Reduce heat to medium-low and cook, stirring frequently, until the vegetables are softened, about 6–8 minutes. Add the minced garlic and tomato paste and cook another 1–2 minutes to develop flavor.

Build the sauce

Slowly whisk in the chicken or seafood stock, a little at a time, until the mixture is smooth and no lumps remain. Add the worcestershire sauce, hot sauce, creole seasoning, smoked paprika, dried thyme and bay leaf. Increase heat to medium and bring to a gentle simmer, stirring occasionally. Simmer uncovered for 8–10 minutes to thicken slightly and meld flavors. Taste and adjust seasoning with salt and pepper.

Add crawfish

Lower the heat to low and stir in the crawfish tails. Cook just until they are heated through, 3–4 minutes — do not overcook, or the tails will become rubbery. Stir in chopped parsley and half of the sliced scallions. Remove and discard the bay leaf.

Finish and serve

Spoon cooked white rice into individual bowls or into a serving bowl. Ladle the crawfish étouffée over the rice. Garnish with the remaining scallions and an extra sprinkle of parsley. Serve immediately with lemon wedges on the side for squeezing, and additional hot sauce if desired.