Heat broth and soy sauce in small heavy, saucepan over low heat until hot. Add half the butter and swirl pan until melted. Add remaining butter and swirl until blended. Remove from heat and cover pan. Place round metal cake rack in large skillet with tight-fitting lid. Pour enough water into skillet to come just under rack and heat to boiling over medium heat. Diagonally cut fillet crosswise in half and center pieces on heatproof plate. Place plate on rack, cover skillet, and steam fish just until opaque at center, about 8 minutes. Remove plate from skillet and blot plate dry with paper towels. Warm sauce and stir in scallions. Spoon sauce over fish and serve hot. Tip: Any white-fleshed fish, such as flounder, can be substituted. Calories per serving: 220; Fat per serving: 12 g fish 16