In a large mixing bowl combine butter, granulated sugar, and brown sugar. Beat on low with an electric hand mixer or in a bowl of a stand mixer until smooth and creamy.
Next, add in your egg and vanilla extract. Mix on low until just combined then set aside.
In a separate large bowl, combine all-purpose flour, cocoa powder, baking soda, and salt. Whisk to combine and gradually add (in batches) to wet ingredients. Mix until just combined, a few lumps are okay.
Last fold in the chocolate chips then cover the bowl with batter with plastic wrap. Place covered batter in the fridge to chill for 1-2 hours. It is important to chill the batter between the batches too.
Preheat your oven to 350 degrees F. Prepare a cooking sheet with nonstick cooking spray or parchment paper. Scoop 2- 2 ½ tablespoonfuls of batter, rolling it into about 2-inch balls.
Arrange the cookie balls on a baking sheet lined with parchment paper at least 2 inches apart but make sure not to press down. Optional: add more chocolate chips to the top of each cookie before baking.
Bake for 10-12 minutes (the time varies due to different ovens).
After baking, the cookies will have a soft center inside. Let the cookies stand in the pan for 5-10 minutes before transferring to a wire rack.