Step 1: Preheat oven to 350°F (175°C) and line baking sheets with parchment paper.
Step 2: In a medium bowl, whisk together flour, cocoa powder, baking soda, and salt.
Step 3: In a large bowl, cream butter, granulated sugar, and brown sugar until light and fluffy.
Step 4: Beat in egg and vanilla extract until well combined.
Step 5: Gradually add dry ingredients to wet ingredients, mixing until just combined.
Step 6: Fold in chocolate chips until evenly distributed.
Step 7: Drop rounded tablespoons of dough onto prepared baking sheets, spacing 2 inches apart.
Step 8: Bake for 10-12 minutes until edges are set but centers are still soft.
Step 9: Let cookies cool on baking sheets for 5 minutes before transferring to wire racks to cool completely.