Preheat oven to 350°F (175°C). Line a baking sheet with parchment paper.
In a bowl, whisk together flour, cocoa powder, baking soda, and salt.
In another bowl, mix melted butter, granulated sugar, and brown sugar until combined.
Add egg and vanilla extract to the butter mixture and mix well.
Gradually add the dry ingredients to the wet ingredients, mixing until just combined.
Fold in chocolate chips.
Drop spoonfuls of dough onto the prepared baking sheet.
Bake for 10-12 minutes or until edges are set.
Let cool on the baking sheet for a few minutes before transferring to a wire rack to cool completely.