1. Preheat the oven to 350 degrees F and line two baking sheets with parchment paper or silicone baking mats.
2. Whisk together the flour, malted milk powder, cocoa powder, baking powder and salt in a medium bowl; set aside.
3. Cream the butter and sugar together on medium speed for about 3 minutes, until very smooth. Add the eggs one at a time, beating for 1 minute after each addition. Beat in the vanilla. Reduce the mixer speed to low and add half the dry ingredients, mixing just until it disappears into the batter. Mix in the milk, then the remaining dry ingredients, mixing only until they are incorporated. With the mixer still on low, or by hand with a rubber spatula, mix in the malted milk balls and chocolate chips.
4. Drop about 2 heaping tablespoonfuls worth of dough (I used a large cookie scoop) onto the sheets, leaving about 2 inches of space between each. Bake for 10 to 12 minutes, until puffed and set but still slightly soft to the touch. Let the cookies rest for 2 minutes before transferring them to a cooling rack to cool to room temperature. Store in an airtight container at room temperature.