Peel shrimp and toss shells with 1/2 tablespoon of Cajun seasoning. Place seasoned shells into a pot with water, 1 tablespoon diced onion, and 1 tablespoon diced bell pepper. Bring to a boil; reduce to a simmer and cover. Let cook for at least 2 hours; the longer it cooks, the more flavor will be in your stock.
Meanwhile, devein shrimp by gently running a knife along the back; this will also make your shrimp plump nicely when cooking. Toss shrimp in remaining Cajun seasoning and place in the refrigerator.
Melt butter in a large pot over medium-high heat. Add flour slowly, stirring constantly with a whisk or wooden spoon. When all flour is added, continue stirring frequently until roux turns brown in color and has a nutty aroma, about 5 minutes. Add remaining onion and bell pepper; saute with roux until onion is translucent, 5 to 7 minutes. Stir in tomato paste.
Stir in tomatoes, okra, and shrimp stock slowly. Add crab boil seasoning. Bring to a boil; reduce heat to a simmer and let cook, uncovered, stirring occasionally, about 1 hour. Stir in shrimp and continue cooking until shrimp are bright pink but not tough, about 20 minutes.
Cook's Notes:
Emeril's(R) or Tony Chacere's Cajun seasoning blend is best. If you do not like okra you can omit, but must use gumbo file powder in its place.
Add shrimp stock slowly. Gumbo should have a stew-like consistency, do not make it too soupy! If you are using pre-cooked/seasoned shrimp, add and turn the burner off; shrimp will be hot in 10 to 20 minutes.
To manage time, prep all your ingredients while stock is cooking. Do not add any extra Cajun seasoning to gumbo pot until after shrimp are added. Shrimp are already seasoned so you may not need it.
Gumbo tastes even better the next day because the flavors have all had a chance to mingle and settle. But keep in mind the spice will be more prevalent.
