Preheat oven to 350°F (175°C). Line baking sheets with parchment paper.
In a large bowl, beat together butter and sugar until creamy and fluffy.
Add eggs one at a time, then stir in vanilla.
In another bowl, whisk flour, cocoa, baking soda, and salt. Gradually add to wet mixture.
Fold in chocolate chips.
Drop rounded tablespoons of dough onto the baking sheets. Leave space—they spread.
Bake for 9-10 minutes until edges are set but centers are soft.
Let cool on baking sheets 5 minutes before transferring to a wire rack.
Try not to eat them all at once.