Toast the pecans: Preheat the oven to 160℃ (320℉), and toast the pecans for 10-15 minutes until fragrant and darkened in colour. Check every few minutes to make sure the pecans are not browning too quickly. Allow to cool and roughly chop.
In a medium bowl, whisk together flour, malted milk powder, salt, baking powder, and baking soda.
Using the paddle attachment of a stand mixer, cream together both sugars and the butter until it's paler in colour and just lightly fluffy – about 2 minutes on medium speed.
Add the egg and vanilla, and paddle together. Scrape the bowl, then continue mixing until very smooth, for about an extra 30 seconds.
Mix in the flour mixture until just barely incorporated with floury bits remaining, then paddle in the milk chocolate and pecans until evenly mixed. Use your hand or a spatula to scrape the bottom of the bowl to ensure no gooey bits remain.
Portion the cookies into 80-90g balls, adding an extra piece or 2 of chocolate on top (a little hat!) and rest, covered, in the fridge overnight.
The next day, preheat the oven to 180℃/350℉.
Bake the cookies for about 16-18 minutes, rotating halfway through baking.
While taking the cookies out of the oven, slam the hot tray onto your bench to flatten your cookie ever so slightly. Sprinkle immediately with flaky salt.
Enjoy warm with a glass of cold milk!
