In a small skillet, toast dry milk powder on stovetop until golden brown, being careful not to let it burn. This should take about 3-4 minutes. Set aside.
Put softened butter, sugar, brown sugar, baking powder, baking soda, and salt in the bowl of a stand mixer and cream until fluffy.
Add eggs and continue mixing until homogenous.
Add flour and toasted milk powder and mix slowly until just combined.
Add chocolate chips and mix slowly again until evenly dispersed.
Scoop using a cookie scoop onto lined baking sheets, leaving about 2 inches between cookies. A 2 tbsp cookie scoop will make about 48 small cookies; a 3 tbsp cookie scoop will make about 32 larger cookies. Bake at 350 degrees for 10-12 minutes.
Optional: Sprinkle lightly with flaky sea salt right after baking. Baked cookies will keep in an airtight container at room temperature for a few days. Unbaked cookie dough can be pre-scooped and kept in the fridge overnight or frozen in a ziploc for a few months.