How to Make It
In a small skillet, toast the fennel, cumin and coriander seeds over moderate heat until fragrant, about 2 minutes; let cool. Transfer to a spice grinder and finely grind the spices.
In a medium casserole, heat the oil until shimmering. Add the carrots, onions, leek, garlic, ginger and chile and cook over moderately high heat until softened and lightly browned, about 5 minutes. Add the ground spices and cook until fragrant, about 2 minutes longer. Add the water, coconut milk and lime leaves and bring to a boil. Stir in the lentils and simmer over low heat, stirring occasionally, until tender, about 20 minutes. Season with salt and pepper.
In a food processor, combine the garlic with the cilantro and mint and pulse until finely chopped. Add the shrimp and pulse until coarsely chopped. Transfer the mixture to a bowl and stir in the cornstarch, 1 tablespoon of fish sauce and the sesame oil. Refrigerate for 30 minutes.
Using slightly moistened hands, roll teaspoons of the shrimp mixture into balls and arrange on a plastic wrap-lined plate.
Add the shrimp dumplings and the 2 teaspoons of fish sauce to the casserole and simmer just until the dumplings are slightly pink and cooked, about 5 minutes. Remove the lime leaves. Stir in the lime juice and cilantro and serve, passing the fish sauce at the table.