In a medium bowl,whisk together the flour, cocoa powder, baking soda, and salt.
Set up a stand mixer with bowl and paddle or hand-held mixer with beaters and large bowl.
Add butter,granulated sugar, and brown sugar.
Beat on medium speed for 5 minutes, until well combined.
Add vanilla and 1egg. Beat for 1 minutes.
Scrape down the sides of the bowl and add 1 egg yolk. Beat 1 minute more.
Add the next yolk and beat for a final minute.
Add dry ingredients and mix until just combined.
Fold in chocolate chips by hand, using a rubber spatula.
Refrigerate dough until lightly chilled.
Roll into 1-inchball and place in the refrigerator for 15 minutes.
Meanwhile, preheat oven to 325 F.
Place cookies on a parchment lined baking sheet. Keep 2-inches between the cookies to allow for spreading. Bake until golden around the edges for 8 to 10 minutes.
Remove from oven and let rest for 2 minutes.
Transfer cookies to a wire rack until cool.
Place in an airtight container for up to 1 week. If you don't eat them first!