1. In a bowl, whisk together heavy cream, lemonade mix, and sugar until mix dissolves. Whisk in cream cheese. Place sponge shell on serving platter and fill with cream-cheese mixture. Arrange blueberries and raspberries in rows on filling. Cut a star stencil from a piece of paper, and place stencil over tart. Dust with confectioners' sugar, then remove stencil.