Combine rice, water, and salt. Bring to a boil, cover, reduce heat, and cook for 15 minutes. Rest covered for 10 minutes, then fluff.
Build the Etouffee:
Season shrimp with 1/2 teaspoon salt and black pepper. Melt butter in a Dutch oven over medium-low heat. Whisk in flour and cook for 8 to 10 minutes, stirring constantly, until the roux is the color of peanut butter.
Add onion, celery, and bell pepper. Cook for 8 minutes, then add garlic, Cajun seasoning, thyme, and cayenne for 1 minute. Gradually stir in warm stock until smooth. Add Worcestershire and bay leaves.
Simmer gently for 15 minutes, stirring occasionally, until the sauce coats a spoon.
Finish:
Add the shrimp and simmer for 4 to 6 minutes, just until opaque and naturally curled. Remove the bay leaves, adjust salt, and stir in half the scallions and parsley.
Spoon over rice and finish with the remaining scallions and parsley.
Notes
Keep the roux moving so it browns evenly without scorching.
Refrigerate for up to two days and reheat gently; avoid boiling once the shrimp are cooked.