Preheat oven to 350°. Line an 8×8 baking pan with parchment paper and set aside.
Melt the butter in a saucepan over medium-high heat. Add the sugar and vanilla, stir well.
Remove pan from heat and whisk in the Hershey’s Special Dark Cocoa Powder.
Gradually pour the chocolate mixture into the bowl that contains the beaten eggs and whisk until well combined.
Gently stir in the flour and chocolate chunks.
Pour batter into the prepared baking pan and bake for 30-40 minutes or until a pick inserted in the center comes out clean. Remove to a wire rack to cool completely. Remove parchment paper (with brownies) from the pan. Peel parchment away but leave brownie sitting on top of it.
Meanwhile, prepare the frosting. In a large bowl, beating butter, powdered sugar, peanut butter, and pinch of salt until light and fluffy. Spread over brownies. Sprinkle with Hershey’s Milk Chocolate Chips, Reese’s Peanut Butter Chips and chopped cashews.