To assemble cake:
Once cooled, run an offset spatula or a small knife around the sides of the pan. Invert the cake onto a serving plate. Pour 1 cup blueberry jam over top of the cake. Cover the jam layer with a generous amount of whipped cream (about 1 cup). Sprinkle with blueberries. Serve remaining whipped cream on the side. Cake can be stored in refrigerator for 2 to 3 days.