1Heat oven to 350°F (325°F for dark or nonstick pan). Make and bake cake as directed on box for 13x9-inch pan. Run knife around sides of pan to loosen cake. Cool completely, about 1 hour.
2While cake is cooling, in medium bowl, gently mix berries, granulated sugar and raspberry liqueur.
3In chilled large bowl, beat whipping cream and powdered sugar with electric mixer on high speed until stiff peaks form.
4Cut or tear cake into 1-inch pieces. In 3-quart glass trifle bowl, arrange half the pieces. Spoon half of the berry mixture over cake; top with half of the whipped cream. Repeat layers. Cover; refrigerate at least 1 hour before serving. Garnish with additional berries if desired. Store covered in refrigerator up to 12 hours.