In the bowl of a stand mixer, beat together the butter, brown sugar, malted milk powder, chocolate syrup, and vanilla for 2 minutes. Beat in the egg until well combined.
In a small bowl, combine the flour, baking soda, and salt and stir to combine.
Gradually add the flour mixture to the wet mixture and mix well.
Stir in the chocolate chunks and chips.
Line a 7x11 baking dish with parchment paper. Press the cookie dough into the dish.
Bake at 375 degrees for 28-30 minutes.
Cool in the pan on a cooling rack.