Preheat oven to 350 F. Line 2 baking sheets with parchment paper.

Add the sugar to a wide, shallow dish (a pie plate works well). In a medium bowl, whisk together the flour, cocoa powder, baking soda, and baking powder.

Add 10 tablespoons of the butter to a microwave-safe bowl and microwave in 20 or 30-second bursts until melted. Stir in the remaining 4 tablespoons of butter until it is completely melted. Set the butter aside for 5-10 minutes to cool until lukewarm, about 90-95 F on an instant-read thermometer.

Add the brown sugar, vanilla, and salt and whisk until incorporated.

Mix in the egg and egg yolk until well combined. Switch to a rubber spatula, and stir in the dry ingredients just until combined.

Shape the dough into balls, each ball should be about 2 tablespoons of dough. Roll the balls in the sugar you put in the shallow dish earlier, coating them on all sides.

Place on the prepared baking sheets, leaving several inches of space in between them. Use the bottom of a glass to press the balls down so each of the cookies has a diameter of about 2 inches. Sprinkle the tops of each cookie with a few pinches of the remaining granulated sugar.

Bake, one sheet at a time, until the cookies are slightly puffy and the edges are just barely set, about 12-13 minutes (the cookies may look slightly undercooked in the center, that's ok). Transfer the baking sheet to a wire rack and let the cookies cool for a few minutes, then remove to a wire rack to cool completely. Continue baking with the remaining dough.