In small bowl, whisk together yogurt and brown sugar; refrigerate.
In chilled mixing bowl, beat whipping cream until it begins to thicken. Add vanilla and beat until stiff peaks form. Fold in yogurt mixture, 1/2 cup strawberries, and 1/2 cup blueberries. Pour into 4 serving dishes, top with remaining fruit and serve.
Tip: Mixture can also be used as filling for pies or tarts.