1. Place shrimp shells and tails in a colander and run under cold water. Drain.

2. In a medium pot, heat 1 tablespoon vegetable oil over medium-high. Add shrimp shell mixture, 1/2 cup each onion and celery, and garlic cloves; season with salt. Cook, stirring often, until shells are pink and mixture is fragrant, 10 minutes. Add 10 cups water and parsley. Bring to a boil, then reduce heat and simmer until flavors develop and stock has reduced to 8 cups, about 45 minutes. Strain through a fine-mesh sieve into a heatproof container.

3. Meanwhile, in a medium pot, whisk together 3/4 cup each vegetable oil and flour to combine. Cook over medium heat, whisking constantly, until roux smells toasted and is the color of butterscotch, about 20 minutes. Set aside. (Make sure to re-whisk roux before using, as it will separate when it cools.)

4. In a large pot, heat 3 tablespoons vegetable oil over medium. Add remaining 1 cup onion and 1 cup celery, along with the bell pepper. Season with salt and pepper. Cook, stirring, until softened, about 10 minutes. Add minced garlic and spices and cook until fragrant, 1 to 2 minutes more. Stir in tomato sauce and shrimp stock. Bring to a simmer, then add in your roux, a few spoonfuls at a time, until combined. Taste and re-season if needed. Simmer, partially covered, about 1 hour. Add crab and shrimp and cook, stirring, until shrimp is just cooked through, 3 to 4 minutes.

5. Heat olive oil in a large skillet over medium-high until shimmering. Add okra and season with salt and pepper. Cook until softened slightly but still crisp and holding its shape, 4 to 5 minutes.

6. Serve gumbo with chopped parsley, sauteed okra, rice, and hot sauce.