Preheat oven to 350 F degrees. Line a 9 inch square baking pan with parchment paper.
Melt butterscotch chips in a small saucepan over low heat, stirring occasionally; set aside.
Beat brown sugar and butter in large bowl until light and fluffy. Beat in eggs, one at a time, scraping down side of bowl after each addition. Beat in melted butterscotch chips and vanilla. Combine flour, baking powder and salt in small bowl; add to butter mixture. Beat until well blended. Spread batter evenly in prepared pan.
Bake 20 to 25 minutes or until golden brown and center is set. Immediately sprinkle with chocolate chips. Let stand about 4 minutes or until chocolate is melted. Spread chocolate chips evenly over the top. Cool completely.
Sprinkle with cocoa if desired. Cut into 2 1/4 inch squares.