Toast the milk powder in advance so it has time to fully cool. Place milk powder in a dry pan and cook over medium heat, stirring constantly, until it turns a yellow color and smells "nutty." I like to toast a lot at a time and then store in an air-tight tupperware container so it's ready whenever I need it.
Preheat oven to 375 degrees
Add the chocolate chips to a rotarty grater and gently grate the chocolate. If you don't have a grater, chop up the chocolate chips with a knife. Set aside.
Measure a cup of flour and add to a mixing bowl. Remove 2 level tablespoons of the flour from the bowl and replace with 2 level tablespoons of the cooled toasted milk powder. It's easiest to measure this way rather than measuring out 14 tablespoons of flour.
Add the fine sea salt and baking soda to the dry ingredients and whisk. Set aside.
To a stand mixer or using a handheld mixer beat softened butter and both sugars for 2 minutes on medium speed.
Add the egg, molasses and vanilla to the bowl and continue beating until fully incorporated. Scrape the bowl and beat again for 20 seconds.
Slowly add the dry ingredients with the mixer on low. Once just combined turn the mixer off. Add the grated chocolate chips and either turn on low for a few seconds or fold by hand.
Line a large sheet pan with parchment paper. Lightly grease the parchment paper with softened butter.
Measure 3 level tablespoons of dough and create a ball. Place 5 balls evenly spaced out on the cookie sheet. Do not flatten.
Cook on the middle rack, one sheet pan at a time, for 7 minutes. Rotate the pan and cook for an additional 90 seconds. Cookies should have golden brown, crinkled edges but be puffy and pale in the center. Sprinkle with flaky salt immediately after baking (optional).
Let the cookies rest on the hot sheet pan for 20 minutes before transferring to a wire rack. Allow to fully cool for several hours to allow the flavor and texture to develop.