Step 1

Melt butter in a large, heavy skillet. Stir in flour; cook and stir over low heat until the color of caramel, about 20 minutes. Add celery, green pepper, and onion; stir until coated. Add stock, water, tomato powder, Cajun seasoning, black pepper, cayenne, and bay leaf. Bring to a boil.

Step 2

Reduce heat; cover and simmer sauce, stirring occasionally, for 30 minutes. Discard bay leaf. Add shrimp and cook until heated through, about 5 minutes.