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 the softened butter and granulated sugar until light and fluffy.

Add the egg and vanilla extract to the butter mixture and mix until combined.

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

Using a cookie scoop, drop dough onto a baking sheet lined with parchment paper.

Bake in the preheated oven for 8-10 minutes, or until the edges are set.

Remove from the oven and let cool on the baking sheet for 5 minutes before transferring to a wire rack.