Melt butter in a large pan over low heat. Gradually whisk in the flour until it forms a paste. Continue cooking, stirring occasionally with a wooden spoon, until it turns a caramel color, approximately 15-20 minutes.
Add your onions, green pepper, celery and garlic and cook over low heat for about 5 minutes or until the veggies get limp.
Add your shrimp and stir to coat in the roux. Then add black pepper, cayenne, Cajun seasoning, green onions, parsley and the Tabasco (to taste).
Add 1 cup of water and stir until incorporated. Add the tomatoes with their juice and stir to blend. Taste for seasoning. Add the salt, starting with 1 t and adding more if needed. Bring the whole mixture to a boil then reduce the heat to low and simmer for about 10-15 minutes, until the shrimp get firm and pink. Once the flavors are nicely blended, you can serve and enjoy!