Broiled Red Snapper with Tamarind Sauce

Name: Broiled Red Snapper with Tamarind Sauce
Ingredients: 1 1/2 tablespoons tamarind from a pliable block; 1/2 cup cold water; 2 small shallots; 3 garlic cloves; 2 teaspoons finely chopped cleaned fresh cilantro roots reserved from Thai Ground-Pork Salad with Mint and Cilantro or cilantro stems; 1 tablespoon Asian fish sauce (preferably naam pla); 1 1/2 teaspoons sugar; 1/4 teaspoon salt; 1/2 teaspoon vegetable oil; two 6-ounce red snapper fillets with skin; 2 scallions; 1 medium or 2 small fresh red chiles (1 to 3 inches long; preferably Thai); about 2 tablespoons fresh whole Thai basil leaves or small fresh regular basil leaves; Garnish: fresh basil sprigs