1 1/2 pounds large shrimp—shelled and deveined, shells reserved
1 small onion, thinly sliced
1 fennel bulb, thinly sliced
2 inner celery ribs, thinly sliced
6 garlic cloves—2 smashed, 4 minced
Pinch of saffron threads, crumbled
1/4 cup Pernod
1/4 cup brandy
1 teaspoon tomato paste
2 tarragon sprigs
2 parsley sprigs, plus 1 tablespoon finely chopped parsley
3 tablespoons unsalted butter
Salt and freshly ground pepper
1 1/2 teaspoons sweet paprika
1 tablespoon chopped cilantro
2 tablespoons fresh lemon juice
In a large pot, heat 2 tablespoons of the oil. Add the shrimp shells and cook over moderate heat until they turn pink, 3 minutes. Add the onion, fennel, celery, smashed garlic and saffron and cook until softened, 5 minutes. Add the Pernod and brandy and cook until evaporated. Stir in the tomato paste, add 6 cups of water and bring to a boil. Simmer until the broth is reduced to 4 cups, 45 minutes. Add the tarragon and parsley sprigs and let stand off the heat for 15 minutes.
Strain the liquid, pressing the vegetables to mash them through the sieve. Alternatively, pass the mixture through a food mill. Discard the shrimp shells. Transfer the liquid to a saucepan and simmer until reduced to 2 cups, 30 minutes. Swirl in the butter and season with salt and pepper.
In a large skillet, heat 1 tablespoon of the oil until shimmering. Season the shrimp with salt and pepper, then sauté over high heat, turning once, until nearly cooked, 2 minutes. Transfer the shrimp to a plate. Add the remaining 3 tablespoons of oil to the skillet. Add the minced garlic and cook over low heat until softened and golden, 1 minute. Stir in the paprika. Return the shrimp to the skillet and add the chopped herbs and the lemon juice. Cook for 1 minute longer, until the shrimp are white throughout.
Ladle the sauce into bowls and top with the shrimp. Drizzle any garlic oil over the shrimp and serve right away.