Combine the first seven ingredients in a large mixing bowl; beat at medium speed for 3 minutes. Pour batter into a greased 13-inch x 9-inch x 2-inch baking pan. Bake at 350 degrees for 30 minutes (top of brownies will appear wet). Cool completely. Combine filling ingredients in a medium mixing bowl; beat until creamy. Spread over cooled brownies. Refrigerate until set. For topping, melt chocolate chips and butter over low heat in a small saucepan. Let cool for 30 minutes or until lukewarm, stirring occasionally. Spread over filling. Chill before cutting. Store in the refrigerator.