Mix your butter and brown sugar on low/medium speed until soft and fluffy.
Continue mixing while adding your eggs, sourdough starter, and vanilla paste.
In a separate bowl, add your flour, baking soda, baking cocoa powder, and salt, and whisk that together.
Turn your mixer to low and slowly add your flour mixture until everything is well incorporated. (Make sure to scrape the sides of the mixing bowl to ensure everything is well blended.)
Stir in your chocolate chips with a mixing spoon.
Cover the bowl and place it into the fridge to chill for 1-24 hours.
Preheat your oven to 375 degrees Fahrenheit.
Scoop the cookies into 3-inch balls and place them onto a cookie sheet covered with parchment paper.
Bake for 13-15 minutes. The bottoms will be brown when ready.
Place on a cooling rack and enjoy once cooled!
