Make the Roux: In a large pot, melt butter over medium heat. Slowly whisk in flour and cook, stirring constantly, until the roux turns medium brown (about 8–10 minutes).
Add Aromatics: Stir in onion, bell pepper, celery, and garlic. Cook for 5–7 minutes until softened.
Season and Simmer: Add broth, diced tomatoes (if using), Cajun seasoning, paprika, cayenne, salt, and pepper. Stir well, then bring to a gentle simmer.
Add Crawfish: Stir in the crawfish tails and cook for 15–20 minutes, allowing the sauce to thicken and flavors to meld.
Finish with Freshness: Add lemon juice, parsley, and adjust seasoning to taste.
Serve: Ladle the Crawfish Etouffee over hot cooked white rice. Garnish with sliced green onions and extra parsley.