Brown butter over medium heat. Add milk powder and cool slightly.
Add miso and whisk to combine. Chill in fridge until soft, but not runny.
Whisk the flour, baking powder, baking soda, and kosher salt together in a large mixing bowl.
Add butter-miso mixture to bowl of stand mixer fitted with the paddle attachment. Add sugar and molasses and beat on medium speed until light and fluffy, about 2-3 minutes.
Add egg and vanilla. Beat on medium-high until pale, fluffy, and aerated, about 4 minutes.
Fold the flour mixture into the dough until just combined.
Fold in the dark chocolate chips.
Chill the dough for at least 3 hours and up to 3 days.
Arrange one oven rack to the top position, and the other to the middle position. Preheat the oven to 350F (180C). Line 2 baking sheets with parchment paper.
Portion the cookies into 1 oz. round balls, arranging them on the trays.
Break each ball in half and squish the halves together so the craggy parts face outwards.
Broil the cookies at 500F (260C) for 1-2 minutes on the upper rack, or until they start to take on some color.
Shift the cookies to the middle rack and bake at 350F (180C) for 10-12 minutes, or until just golden around the edges.
Remove the cookies from the oven. While they're still hot, use a glass to gently swirl the cookies and shape them into perfect circles (optional).
Allow the cookies to cool for at least 15 minutes on the pan. Transfer to a wire rack to cool completely.