Preheat oven to 375°F (190°C). Line baking sheets with parchment paper.

Cream together the softened butter, granulated sugar, and brown sugar until light and fluffy using an electric mixer.

Beat in the eggs one at a time, then stir in the vanilla extract.

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

Gradually add the dry ingredients to the wet ingredients, mixing until just combined. Do not overmix.

Stir in the chocolate chips.

Drop by rounded tablespoons onto the prepared baking sheets, leaving about 2 inches between each cookie.

Bake for 9-11 minutes, or until the edges are set and the centers are still slightly soft.

Cool on baking sheets for a few minutes before transferring to a wire rack to cool completely.

Melt the black candy melts. Use a toothpick to draw spider legs onto the cooled cookies. Add candy eyeballs if desired. Let the spider legs set completely.