Coarsely puree nectarines in blender or food processor with lemon juice. Stir into sugar; set aside. In large chilled mixer bowl , mix whip cream, vanilla and salt until stiff. Fold in nectarine mixture. Turn into 9x9x2-inch pan. Freeze uncovered until set at edges, about 1 hour. Beat until smooth. Freeze until firm, then cover airtight. Remove from freezer about 15 minutes before serving.