Steamed Fish with Lime and Chile

In a clay mortar, lightly pound garlic, cilantro stems, and chiles with a wooden pestle until a coarse paste forms. Add 2 tablespoons lime juice, fish sauce, sugar, and pepper; mix with a spoon to combine. (Alternatively, pulse in a mini-processor until a loose paste forms.) Set sauce aside. Place fish on a plate that will fit inside the steamer with some wiggle room; pour reserved paste over. In a wide pot, add water to a depth of 1". Bring to a boil. Transfer fish on plate to steamer. Set steamer over pot and pour chicken broth over fish. Cover; steam fish until cooked through, 12-15 minutes. Using 2 large spatulas, transfer fish to a serving platter. Spoon juices on plate in steamer over fish. Drizzle with lime juice, if desired. Garnish with lime slices and cilantro leaves. Serve with steamed rice.