Preheat the oven to 350 degrees.
Spray a 9in round cake pan with nonstick spray.
Cream together your butter and sugars in a large bowl, for about 2 minutes, till light in color and smooth.
Add in the egg and egg yolk and the vanilla and stir in to the creamed butter.
In another bowl mix together your baking soda, salt and flour.
Add your dry ingredients to your wet ingredients and stir everything together till just combined.
Add in the chocolate chips and m&ms and fold into the batter.
Press the cookie dough into the prepared cake pan.
Bake in the preheated oven for 18-24 minutes until the cookie is golden brown and baked throughout.
Press some m&ms on top of the cookie to look nice.
Allow to cool for in the pan. Loosen the sides with a knife and put cake onto a platter or serving dish.
Starting in the middle draw 6 to 8 lines out from the middle to the outside of the cookie with the black icing.
Connect the lines with the icing to make it look like a spider web.
Top with plastic spiders.
Slice and serve.