First, add 3-oz. of dark chocolate pieces (set the rest aside) and 2 tablespoons of butter into a bowl of a double boiler or a microwave safe bowl. Melt the chocolate until it is glossy and smooth.* Set aside.
Next, mix the dry ingredients. Add the all-purpose flour, cocoa powder, baking soda, and salt to a bowl. Whisk all of the ingredients together until they are well combined.
Add 1-oz. of chopped bittersweet chocolate pieces and all of the chopped milk chocolate pieces to the flour mixture. Toss into the flour and set aside.
Add the rest of the butter and brown sugar to the bowl of a standing mixer. Beat on medium/high speed for 3-5 minutes until the mixture turns light in color and is creamed and fluffy. Be sure to scrape the sides throughout the beat time.
Meanwhile, add the eggs and vanilla to a separate bowl and gently whisk the eggs together so the egg yolk, egg white, and vanilla are combined.
Slowly add the egg mixture to the creamed butter and sugar and beat until the egg combines with the sugar and butter and becomes light and fluffy.
Slowly add the dry ingredients to the wet ingredients and mix until just combined. Be sure there are no flour clumps at the bottom of the mixing bowl.
Finally, add the melted chocolate to the cookie dough and mix the melted chocolate in with the cookie dough.
Transfer the cookie dough into an airtight container and refrigerate the dough for at least 2 hours or overnight, for best results.
Remove the cookie dough from the refrigerator and let it sit at room temperature for 10 minutes.
Preheat the oven to 350ºF and line a baking sheet with parchment paper.
While the dough is sitting, add the granulated sugar to one bowl and the powdered sugar to a separate bowl.
Use a tablespoon scoop to scoop a tablespoon of cookie dough into your hands and roll the dough into a ball.
Roll the dough in the granulated sugar and then the powdered sugar until the ball is completely covered. Place the dough on the lined baking sheet and repeat until all the dough has been rolled in both sugars.
Be sure to space the cookie dough balls far enough apart, these cookies do spread a little bit.
Bake at 350ºF for 9-11 minutes. The crinkle cookies should begin to crack on the tops when they are almost done.
Remove the cookies from the oven and transfer them to a cooling rack.