Angel Berry Tunnel Cake

1 prepared angel food cake (10 inches)
1-1/2 cups fresh or frozen raspberries, thawed and drained
1-1/2 cups fresh or frozen blueberries
8 cups whipped topping
Additional berries, optional

With a serrated knife, slice off the top 1/2 in. of the cake; set aside. Cut a tunnel about 2 inches deep in the cake, leaving a 3/4-in. shell. Remove cake from tunnel; cut into 1-in. cubes.

Combine cake cubes, berries and half of the whipped topping; spoon into tunnel. Replace cake top. Frost with remaining whipped topping. Garnish with berries if desired. Refrigerate until serving. Makes 12 servings.