In a medium bowl, sift the flour, cocoa powder, baking soda, and salt. Set aside. In a microwave safe bowl, melt the chocolate bar in 20 second intervals, mix well in between.
2 1/2 cups All-purpose flour, 1/3 cup Unsweetened cocoa powder, 1 tsp Baking soda, 1 tsp Salt, 4 oz Semi sweet chocolate bar
Using a mixer in a large mixing bowl, beat the melted butter, brown sugar, and sugar on high speed for 2 minutes. It will lighten in color.
1 cup Unsalted butter, 1 cup Light Brown sugar, 1/2 cup White granulated sugar
Add in the melted chocolate, eggs, and vanilla. Beat on high speed for 1 minute.
2 Large eggs, 1 tsp Pure vanilla extract
Add in the dry ingredients and mix on low speed until just combined. Add in the dark chocolate chips and milk chocolate chips and mix.
3/4 cup Dark chocolate chips, 3/4 cup Milk chocolate chips
Let the dough sit for 10 minutes before scooping. This allows the gluten to form which helps with spreading, it also makes the dough less sticky.
Prepare two cookie sheets with parchment paper. On one cookie sheet, use a large cookie scoop to scoop the dough and place on the cookie sheet. Top all the cookie dough balls with extra chocolate chips. Chill all of the cookie dough balls in the fridge for 10 minutes while the oven preheats.
Preheat the oven to 350℉. Bake 6 cookie dough balls at a time. Bake for 13-15 minutes until the edges are set.
Let the cookies sit on the hot pan for 5 minutes before transferring to a cooling rack.