1. Preheat the oven to 350°F/180°C.
2. Butter or use baking spray to grease cookie sheets or line with parchment paper.

For the chocolate cookies:

1. Sift flour, cocoa powder, and baking soda into a medium bowl. 
2. In a separate large mixing bowl, beat butter with sugar and vanilla extract until creamy, about 2 minutes.
3. Add eggs, one at a time, and beat until combined.
4. Add the dry ingredients and whisk until thoroughly integrated. Don't beat at this point so the dough remains tender. 
5. Fold in the chocolate chips.
6. Scoop portions of cookie dough and roll them into balls.
7. Place on the prepared cookie sheet, an inch and a half or two apart. 
8. Bake for 12-15 minutes, until they puff and crackle. The tops will be dried. 
9. Let cool completely on a wire rack. 

For the spider web:

1. Melt the marshmallows in a bowl and mix with a fork until smooth.
2. You can use gloves for this part or get your hands messy. 
3. Take some melted marshmallow mixture and use your fingers to pull it apart and create strings. Place over the cookies, creating a web and pinching the edges. 
4. Let dry on a wire rack. 
5. You can add eyeball candies.