Preheat oven to 180°C (350°F) and line a baking sheet with parchment paper.
In a bowl, mix flour, cocoa powder, baking powder, and salt.
In a separate bowl, cream the butter, brown sugar, and white sugar until fluffy. Add the egg and vanilla essence.
Gradually add the dry ingredients to the wet ingredients and mix to form a dough.
Roll dough into small balls and place on the baking sheet. Slightly flatten each cookie.
Bake for 10-12 minutes, until firm around the edges. Let cool completely.
Add a chocolate ball or Malteser to the center of each cookie.
Pipe melted chocolate to create spider legs and add candy eyes.