Preheat oven to 350. Line a 13 x 9 inch pan with foil or parchment and set aside.
In a medium saucepan, melt butter over low heat. Stir in chocolate chips, and melt, stirring frequently. When there are no more lumps, remove from heat and stir in sugar and vanilla. Add the eggs one at a time, and mix until the mixture is smooth and glossy. Fold in the cocoa powder, salt, and flour, and mix until barely combined.
Pour the mixture into the prepared pan and bake 30-35 minutes, or until a toothpick inserted one inch from the side of the pan comes out clean. Remove from oven and allow to cool completely.
When the brownies are cool, beat together the softened butter, peanut butter, powdered sugar, and vanilla. Add milk until the frosting reaches a smooth consistency. Spread the frosting over the cooled brownies.
Add the chocolate chips and butter to a small microwave bowl. Microwave at 50% power for 30 second intervals, stirring in between, until melted and smooth. Pour into a piping bag (or Ziploc bag), cut off a small corner of the bag, and drizzle the chocolate over the frosting. Sprinkle with the Reese's candies. Let cool and set up before serving.