In a mixing bowl, cream the softened butter, brown sugar, and granulated sugar until smooth and fluffy.
Add the egg and vanilla extract. Mix until fully combined.
In a separate bowl, combine flour, cocoa powder, baking soda, and salt.
Gradually add the dry ingredients to the wet mixture. Mix until a soft dough forms. Fold in chocolate chips if using.
Scoop small portions of dough and roll into balls. Place them on a lined baking tray, leaving space between each.
Preheat oven to 180°C (350°F) and bake for 10 to 12 minutes until edges are set.
Transfer biscuits to a cooling rack and let them cool completely to set the texture.
