In a mixing bowl, whisk together the flour, baking powder, salt and malted milk powder.
In the bowl of an electric mixer fitted with the paddle attachment, beat the butter and brown sugar on medium speed until completely combined. Scraping down the sides of the bowl, add the eggs and vanilla. Beat until combined.
Add the flour mixture in 2 batches and beat until just combined. Add the malted milk balls, chocolate chips and walnuts and beat until just combined, about 10 seconds.
Pour the mixture into a buttered 9 by-13-inch baking pan. Bake for 25 to 30 minutes, or until a toothpick inserted into the center of the blondie comes out clean.
Transfer to a wire rack and let cook for 20 minutes. Cut the blondies into squares and serve with ice cream.