Shrimp Étouffée

Melt 1 tablespoon butter in Dutch oven over medium heat. Add shrimp shells, 2 cups onion, 1/2 cup celery, and 1 teaspoon salt and cook, stirring occasionally, until shells are spotty brown, about 10 minutes. Add water, smashed garlic, peppercorns, bay leaves, and thyme sprigs and bring to boil. Reduce heat to low, cover, and simmer for 30 minutes. Strain shrimp stock through fine-mesh strainer set over large bowl, pressing on solids to extract as much liquid as possible; discard solids. Wash and dry pot. (Stock can be refrigerated for 3 days or frozen for up to 1 month.)

Toast flour in now-empty pot over medium heat, stirring constantly, until just beginning to brown, about 5 minutes. Whisk in remaining 8 tablespoons butter until melted and combined with flour. Continue to cook, whisking constantly, until deep brown, 4 to 6 minutes.

Add bell pepper, remaining onion, remaining celery, 1 teaspoon salt, and 1/2 teaspoon pepper and cook, stirring often, until vegetables are softened, 10 to 12 minutes. Add paprika, cayenne, minced garlic, and minced thyme and cook until fragrant, about 1 minute. Stir in tomatoes and their juice and cook until dry, about 1 minute. Slowly whisk in 4 cups shrimp stock until incorporated (reserve any remaining stock for another use). Bring to boil, reduce heat to medium-low, and simmer until slightly thickened, about 25 minutes.

Season shrimp with salt and pepper, add to pot, and simmer until cooked through, about 5 minutes. Stir in scallions and Worcestershire. Season with salt and pepper to taste. Serve over rice with hot sauce and lemon wedges.