In a medium mixing bowl stir together buttermilk and cake and pastry filling. Pour the mixture into an 8x4x2-inch loaf pan. Freeze about 3 hours or till firm.
Break frozen buttermilk mixture into chunks. Transfer to a chilled large mixing bowl. Beat with an electric mixer on medium to high speed till smooth but not melted. Return to cold pan. Cover and freeze 6 hours or till firm. To serve, scoop into dessert dishes.