Spray a 9x9 inch baking pan with cooking spray and line with parchment paper. Let paper extend over two sides for easy removal of brownies.
Melt the bittersweet chocolate and butter together in a microwave safe container. Heat on high for 30 seconds, stir. Repeat. Let sit for a few minutes and stir again. Chocolate should be smooth and completely melted. If not, heat on 50% power in 15 second intervals until melted.
Beat eggs and sugar together in a medium bowl with a fork.
Mix in salt and vanilla extract. Stir in melted chocolate. Stir in flour just until combined.
Pour batter into prepared pan and smooth top with an offset spatula. Bake for 20 to 25 minutes or until center has set. Do not over bake.
Let brownies cool completely before frosting.
Ganache Frosting
Combine chocolate chips and whipping cream in small saucepan. Stir over low heat until chocolate has melted and cream is completely combined.
Pour over cooled brownies. Refrigerate until frosting has set up completely.
Using on oval cookie cutter (round or egg shape will also work), cut out as many spider bodies as you can. Decorate with candy eyes, cinnamon candies, and chocolate jimmies. Cut black licorice into strips and insert into the brownies for spider legs.
Chill until ready to serve. Leftovers should be stored in an airtight container.