How to Make It
Cut chicken breasts in half crosswise through the bone. Using the tip of a knife, cut deep slits in skin sides of chicken at 1-inch intervals. Sprinkle chicken all over with 1 tablespoon salt, rubbing into slits. Stir together coconut cream, scallion, minced cilantro, grated ginger, 2 table-spoons fish sauce, garlic, minced chiles, and lime zest in a bowl; rub all over chicken and into slits. Refrigerate 30 minutes.
Meanwhile, stir together chicken stock, sliced ginger, remaining 1 tablespoon fish sauce, whole chiles, and lime juice in a large, deep skillet or pot; bring to a boil over medium-high. Reduce heat to medium. Sprinkle sweet potatoes evenly with remaining 11/2 teaspoons salt. Spread sweet potatoes inside 1 basket of a 2-tier, 9 1/2-inch round bamboo steamer; fit basket inside skillet. Cover and steam 10 minutes.
Uncover sweet potatoes. Arrange chicken, skin sides up, in second steamer basket; fit on top of sweet potato basket. Cover and steam over medium until sweet potatoes are tender and a thermometer inserted in thickest portion of chicken registers 155°F, about 20 minutes. Remove from heat.
Transfer chicken and sweet potatoes to plates. Garnish with cilantro sprigs and flaked coconut; serve with lime wedges.