Step 1 - Cake procedure: Bake cake according to directions on box and cool overnight.
Step 2 - Whipped Cream procedure: Whip the heavy cream in a chilled mixing bowl on half speed for 4 minutes until the cream begins to thicken. Increase the speed to high and whip until soft peaks form.
Turn off the mixer and scrape the bowl. Add the sugar and the vanilla. Mix until the sugar is absorbed and stiff peaks form.
Step 3 - Topping procedure: Split the layers in half and spread the preserves over 3 layers, but not the top layer.
Assemble the cake by spreading equal amounts of cream and stacking the layers. Place the top layer on the cake and spread the whipped cream on the sides.
Top the cake with the remaining cream and decorate with berries and rosettes of cream if desired.