Preheat oven to 350 degrees F (175 degrees C). Line a 9x13 inch baking pan with foil and grease the foil.
In a medium saucepan, over low heat, combine 3/4 cup butter with semisweet and unsweetened chocolate. Cook, stirring frequently, until everything is melted and smooth. Remove from heat and stir in the sugar and 1 tablespoon vanilla. Beat in the eggs one at a time, mixing well after each. Combine the flour, baking soda and salt; stir into the chocolate mixture. Spread the batter evenly into the prepared pan.
Bake in the preheated oven for 25 to 30 minutes, until a toothpick inserted into the center comes out clean. Cool in pan on top of a wire rack.
To make the topping: In a medium bowl, mix malted milk powder, milk and 1 teaspoon vanilla until smooth. Beat in the butter and confectioners' sugar until well blended. Spread over cooled bars. Sprinkle crushed malt balls over the top. Cut into bars and serve.