Preheat the oven to 350°F (175°C).

In a mixing bowl, whisk together the flour, cocoa powder, baking soda, and salt.

In another bowl, cream together the softened butter, granulated sugar, and brown sugar until light and fluffy.

Beat in the egg and vanilla extract until well combined.

Gradually add the dry ingredients to the wet ingredients, mixing until just combined.

Fold in the chocolate chips if using.

Drop tablespoon-sized balls of dough onto a baking sheet lined with parchment paper.

Bake in the preheated oven for 10-12 minutes, or until the edges are set.

Allow cookies to cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.