Ingredients

• 1 1/2 lb jumbo (8 to 12 per lb) shrimp
• 3 teaspoons sea salt dissolved in 11/2 cups water
• 1 tablespoon tamarind from a pliable block
• 1/3 cup water
• 1 tablespoon peanut oil
• 1 tablespoon chopped cleaned fresh cilantro roots and/or stems, pounded to a paste
• 1 tablespoon minced garlic
• 1 tablespoon Sriracha or other Asian hot chile sauce
• 1 1/2 tablespoons palm sugar, or to taste
• 1 tablespoon Asian fish sauce (preferably Thai naam pla), or to taste
• Garnish: 2 fresh serrano or jalapeño chiles, seeded, halved lengthwise, and finely julienned crosswise; and fresh cilantro sprigs

Instructions

1. Prepare grill for cooking.
2. Soak shrimp (still in shells) in salt water 5 minutes, then rinse well in a colander.
3. Make sauce: Place tamarind in a bowl with water and rub with your fingers to dissolve pulp. Pour through a sieve into a bowl, pressing hard on solids, and discard solids. Heat oil in a small heavy saucepan over moderate heat until hot but not smoking, then cook cilantro paste and garlic, stirring, until fragrant. Stir in hot sauce, 3 tablespoons tamarind juice, palm sugar, and fish sauce. Simmer until thickened to consistency of light syrup, about 3 minutes.
4. Place tamarind in a bowl with water and rub with your fingers to dissolve pulp. Pour through a sieve into a bowl, pressing hard on solids, and discard solids.
5. Heat oil in a small heavy saucepan over moderate heat until hot but not smoking, then cook cilantro paste and garlic, stirring, until fragrant. Stir in hot sauce, 3 tablespoons tamarind juice, palm sugar, and fish sauce. Simmer until thickened to consistency of light syrup, about 3 minutes.
6. Grill shrimp: Snip shells of shrimp with scissors down center of back, from wide end to second-to-last tail section. Butterfly shrimp in their shells, making a deep incision along length of back where shells are cut, and devein. Grill shrimp on their sides on an oiled rack set 5 to 6 inches over glowing coals until shells are pink and slightly charred and shrimp are just cooked through, 3 to 4 minutes on each side. (Alternatively, grill shrimp in a hot well-seasoned ridged grill pan over moderate heat.) Spoon tamarind sauce over shrimp (still in shells) in a serving dish.
7. Snip shells of shrimp with scissors down center of back, from wide end to second-to-last tail section. Butterfly shrimp in their shells, making a deep incision along length of back where shells are cut, and devein.
8. Grill shrimp on their sides on an oiled rack set 5 to 6 inches over glowing coals until shells are pink and slightly charred and shrimp are just cooked through, 3 to 4 minutes on each side. (Alternatively, grill shrimp in a hot well-seasoned ridged grill pan over moderate heat.)
9. Spoon tamarind sauce over shrimp (still in shells) in a serving dish.