Caribbean Mango and Steamed Shrimp Salad

Name: Caribbean Mango and Steamed Shrimp Salad
Ingredients: 1 stalk of fresh lemongrass, tender inside only; 3 tablespoons canola oil; 2 garlic cloves, thinly sliced; 1 shallot, thinly sliced; 1 tablespoon chopped fresh ginger; 1 1/2 pounds large shrimp, shelled and deveined, shells reserved; 1 tablespoon tomato paste; 1/2 cup dry white wine; 3 cups water; 2 tablespoons fresh lime juice; Salt; Freshly ground pepper; Cayenne pepper; 1 1/2 teaspoons minced tarragon; 3 mangoes (about 14 ounces each), peeled and cut into 1/2-inch dice