Preheat oven to 350 degrees F. Line an 8x8 pan with aluminum foil and spray with cooking spray. 

In a large bowl, melt chocolate and butter, and stir to combine. (To melt, microwave in 30 second intervals, stirring in between.) Add in granulated sugar and brown sugar, and stir to combine. Add in egg, egg yolk, and vanilla, flour and salt. Stir brownie batter to combine.  

Pour batter into the prepared 8x8 pan. Bake at 350 degrees F for 25-30 minutes, or until set. Let brownies cool, and enjoy!