Preheat oven to 350 °F and grease 6 mini loaf pans.
Melt butter and unsweetened chocolate together in microwave, stirring every 10 seconds. Let stand 5 minutes. Whisk buttermilk, egg and vanilla into butter mixture. In a separate bowl, sift flour, sugar, malted milk powder, baking powder and salt. Make a well in center of dry ingredients and pour in butter mixture. Stir just until blended. Fold in milk chocolate chunks and malted milk balls and spoon into prepared loaf tins. Bake for 35 to 40 minutes, until a tester inserted in the center of the loaves comes out clean. Let cool for 15 minutes, then turn out onto a rack to cool completely.