Step 1

In a mixing bowl, sift together flour, cocoa powder, cornstarch, baking soda, and salt. Set aside.

Step 2

In a microwave safe bowl, heat chopped chocolate for 30 seconds. Stir well. Heat for 20 seconds. Stir well. Heat for 15 second intervals until chocolate is melted. Set aside.

Step 3

Using a mixer, beat the butter, sugar, and brown sugar together for 2 minutes on high. Butter should be smooth and fluffy. Add in vanilla and melted chocolate. Beat on high for 2 minutes.

Step 4

Then, add in egg and egg yolk. Beat on high for 1 minute.

Step 5

Slowly add in the dry ingredients. Mix until combined. Add in the white chocolate chips and semi-sweet chocolate chips. The dough should be thick but wet.

Step 6

Cover and chill in the fridge for 30 minutes. Preheat oven to 350°F. Prepare 2 cookie sheets with parchment paper.

Step 7

Use a large cookie scoop (3oz) and scoop the dough directly on the cookie sheet. Separate cookie dough 3 inches apart on cookie sheet. Bake 6 per cookie sheet.

Step 8

Bake for 13-15 minutes. Since it is chocolate it will be hard to tell when it is done. The edges should be set and slightly firm. If it is too hard, then it is over baked. Let the cookies chill on cookie sheet for 5 minutes before transferring to a cooling rack. Top with extra chocolate chips.