Preheat oven to 350 degrees F (175 degrees C). Grease an 8x8 inch baking pan. In a bowl over a pan of simmering water, or in the microwave, melt the unsweetened chocolate, stirring occasionally until smooth. Set aside to cool.
In a medium bowl, cream together the shortening and white sugar until light and fluffy. Beat in the eggs, one at a time then stir in the vanilla. Mix in the melted chocolate Combine the flour, 1/2 cup chocolate malt powder, baking powder and salt; stir into the chocolate mixture. Spread evenly into the prepared pan.
Bake for 20 to 25 minutes in the preheated oven, until set. Let bars cool in the pan before frosting.
To make frosting, cream together the butter, 1/4 cup of malt powder and salt. Gradually beat in the confectioners' sugar and heavy cream until smooth and spreadable. Spread over cooled bars before cutting into squares.