Melt 4 tablespoons unsalted butter in Dutch oven over medium heat.
Sprinkle ¼ cup all-purpose flour over top, reduce heat to medium-low, and cook, stirring constantly until flour is color of cinnamon, about 10 minutes.
Stir in 1 finely chopped small onion, 2 thinly sliced celery ribs, 1 finely chopped small bell pepper, and ½ teaspoon table salt and increase heat to medium.
Cook, stirring often, until vegetables are softened, about 8 minutes.
Stir in 2 tablespoons tomato paste, 1 teaspoon paprika, 4 minced garlic cloves, ¼ teaspoon cayenne pepper, 1 teaspoon dried thyme, 1 teaspoon Old Bay seasoning, and 2 bay leaves.
Cook until fragrant, about 2 minutes.
Stir in 4 cups seafood stock, 1 (14.5-ounce) can diced tomatoes, and remaining ½ teaspoon salt.
Bring to vigorous simmer, then reduce heat to medium-low and simmer until thickened slightly, about 20 minutes.
Stir in 8 ounces large shrimp and 8 ounces lump crab meat.
Increase heat to medium-high and return to brief simmer, then remove from heat and let sit until shrimp are opaque throughout, about 5 minutes.
Remove bay leaves.
Stir in 2 tablespoons chopped fresh parsley, 1 tablespoon lemon juice, and 1 tablespoon Worcestershire sauce and season with salt and pepper to taste.
Serve with lemon wedges and hot sauce.
