1. In a medium bowl, whisk together the flour, cocoa powder, baking soda, and salt.
2. In a large bowl, beat together the butter, brown sugar, and granulated sugar until creamy. Add the egg and vanilla extract, mixing well.
3. Gradually mix in the dry ingredients until just combined. Fold in the chocolate chunks.
4. Preheat the oven to 350°F (175°C). Line a baking sheet with parchment paper.
5. Scoop tablespoon-sized portions of dough onto the prepared baking sheet.
6. Bake for 10-12 minutes, until the edges are firm but the center is soft.
7. Allow to cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.

Notes:
For an extra rich flavor, choose high-quality cocoa powder and chocolate chunks. For a variation, consider adding nuts or experimenting with different types of chocolate.