Preheat your oven to 350°F (175°C).
In a bowl, whisk together flour, cocoa powder, baking soda, and salt.
In another bowl, cream together the softened butter, granulated sugar, and brown sugar until fluffy.
Add the egg and vanilla extract to the butter mixture, beating until well combined.
Gradually mix the dry ingredients into the wet ingredients until just combined.
Fold in the chocolate chips gently.
Using a spoon, scoop dough onto a baking sheet lined with parchment paper.
Flatten each cookie slightly and create a small indent in the center.
Place a chocolate square in the center of each cookie.
Bake for 10-12 minutes or until the edges are set but the center is still soft.
Let them cool on the baking sheet for a few minutes before transferring to a wire rack.