Preheat oven to 350°. Grease and flour 10-inch cast-iron skillet. In medium bowl, whisk first 5 ingredients. In large bowl, whisk molasses and butter. Whisk in buttermilk and egg, then flour mixture. Pour into skillet. Bake until cake springs back when gently pressed, 35 to 40 minutes. Let cool for 15 minutes. Cut into wedges; garnish.