For the cupcakes: 1 ½ ounces semi-sweet chocolate, chopped ¼ cup prune juice ¾ cup all-purpose flour ¾ cup sugar ½ cup unsweetened cocoa powder ¼ teaspoon baking soda ¼ teaspoon baking powder ¼ teaspoon salt 1 large egg 1 large egg yolk 1/3 cup buttermilk ¼ cup vegetable oil ½ teaspoon vanilla extract For…