In the bowl of a stand mixer, add the butter, granulated sugar, and brown sugar. Mix on low speed until light and fluffy, about 5 minutes, while periodically scraping down the sides of the bowl.
Pour in the vanilla extract and whole egg and mix on low until just incorporated. Add in the additional egg yolk and mix until incorporated. Do NOT overmix.
In a separate bowl, whisk together the bread flour, Dutch-processed cocoa powder, baking powder, and salt until well combined. Add these dry ingredients to the wet ingredients in three stages, rather than adding all at once.
Sprinkle in the chocolate chips and mix until the chips are evenly dispersed throughout the dough. Cover the bowl with plastic wrap and chill for at least 3 hours or overnight. When ready to use, remove the dough from the fridge and allow to come to room temperature, about 20 minutes. Meanwhile, preheat the oven to 350 ℉.
Pour about 50g of granulated sugar in a small bowl and 75g of powdered sugar in another. Use a tablespoon-sized cookie scoop to measure out each dough ball before generously rolling in the granulated sugar, then the powdered sugar, until fully coated.
Place dough balls on a lined cookie sheet, leaving about 2 inches in between. Bake for 10-12 minutes, until centers are fudgy but don't look raw (I had great success at 11 minutes).
Allow cookies to cool on the tray for five minutes before dusting with more powdered sugar. Transfer cookies to a wire cooling rack until cooled completely.
