1. Preheat oven to 350°F. Grease bottom only of 13x9-inch pan with cooking spray or shortening (for easier cutting, line pan with foil, then grease foil on bottom only of pan). Make brownies as directed on box for 13x9-inch pan. Cool completely, about 1 hour.
2. Reserve 1/4 cup chocolate chips for drizzle. In large microwavable bowl, place remaining chocolate chips and 1 1/4 cups whipping cream. Microwave uncovered on High 2 to 3 minutes, stirring once every minute, until chocolate is melted. Stir until mixture is smooth. Refrigerate about 20 minutes or until slightly thickened.
3. Add frosting to chocolate mixture. Beat with electric mixer on high speed 1 to 2 minutes or until well blended and soft peaks form. Spread over cooled brownies, smoothing top.
4. In small microwavable bowl, microwave reserved 1/4 cup chocolate chips and 1 tablespoon whipping cream uncovered on High 30 to 45 seconds, stirring once, until mixture can be stirred smooth. Drizzle over frosting mixture. Refrigerate 1 to 2 hours or until set.
5. Cut into 12 squares; cut each square diagonally in half to make triangles. Garnish with raspberries.