Step 1

Using a hand-held mixer or stand mixer, cream butter and sugars for 3 minutes on medium speed until fluffy and pale. Mix in egg and vanilla, scraping down the bowl as needed.

Step 2

In a separate bowl, whisk together flour, cocoa powder, cornstarch, baking soda and salt. Slowly mix the dry into the wet ingredients on low speed until combined. The dough will be thick. Add the chocolate chips and mix until evenly distributed (5-10 seconds.)

Step 3

Cover dough with plastic wrap and chill for at least 1 hour, and up to 24 hours.

Step 4

When ready to bake, remove cookie dough from the refrigerator and allow to sit at room temperature for 10 minutes. Preheat oven to 350°F. Line 2 baking sheets with parchment paper or silicone baking mats. Set aside.

Step 5

Roll balls of dough, about ¼ cup-sized of dough each, into balls (the dough will be crumbly, but forms easily,) the flatten them with your palm. Place no more than 6 cookies one each baking sheet.

Step 6

Bake for 10-11 minutes, until the middles look only slightly wet and soft. Cool for 5 minutes on pans, then remove to cooling rack to cool completely. The cookies will slightly deflate as you let them cool.