These Butterfinger Brownies are rich and fudgy, with the signature crispety, crunchety, peanut buttery-ness of Butterfingers! Don't wait until you have leftover Halloween candy to make these! Make sure you grab an extra bag of Butterfingers Peanut Butter Cups to have on hand just for baking these frightfully delicious Halloween brownies!
Preheat oven to 350 degrees. Line a square 8x8" baking dish with parchment paper and spray with cooking spray.
Sift together the flour, cocoa powder, and salt in a bowl.
Combine the butter and chopped unsweetened chocolate in a large microwave-safe bowl. Microwave on high in 30 second bursts, stirring well with a spoon or spatula between bursts, until completely melted and smooth. Allow to cool for a few minutes.
In a separate bowl, combine the eggs, egg yolk, and sugar and beat with an electric mixer for 3 minutes on medium-high speed until light and thick. This step is important because it is what is going to give that papery thin, crackly crust and perfect brownie texture that you want. Add the vanilla and beat again until combined.
Add the slightly cooled melted chocolate and butter to the eggs, sugar and vanilla and stir to combine using a wooden spoon or spatula. Sprinkle the sifted flour, cocoa powder and salt over the batter and gently stir it in, just until no streaks of flour remain. Stir in the chopped Butterfingers and Butterfinger Peanut Butter Skull Cups.
Pour the brownie batter into the prepared baking dish and bake for 35 to 40 minutes, until a toothpick or skewer inserted into the center of the brownies comes out mostly clean with only a few crumbs attached. Be sure not to overbake.
Cool completely before cutting.