Using electric mixer, beat cream in medium bowl to soft peaks. Gently fold in remaining cream in 2 batches. Using clean dry beaters, beat egg whites and cream of tartar in another medium bowl until frothy. Gently fold in remaining whites in 2 batches. Cover bowl with plastic and refrigerate mousse 8 hours or overnight.
Spoon mousse into pastry bag fitted with large star tip.
Pipe mousse into goblets or wine glasses. Top mousse with fresh mint sprigs and serve.