Preheat the oven to 350 degrees F. Grease an 11x7 inch pan and line with parchment if desired.
Combine the flour, baking powder, salt and malted milk powder; stir well and set aside.
Beat the butter and brown sugar until creamy. By hand or using lowest speed of your mixer, stir in the egg and vanilla (don’t beat the egg too much); Stir flour mixture into butter mixture in three parts. When last flour addition is almost blended, add malt balls, chocolate and nuts and mix until flour disappears. The batter is pretty thick.
Scrape batter into pan and spread evenly.
Bake in the center of the oven for 20-22 minutes, or until a toothpick inserted into the center of the blondies comes out clean.
Transfer to a wire rack and let cool. Grasp foil, lift from pan and score into 12 bars. The guys from Bake say these are good warm. I'm sure they are, but I liked them better after they’d set.