EMPTY 1 pkg. of the gelatin into medium bowl. Add sugar; mix well. Gradually add 2/3 cup boiling water, stirring at least 2 min. until completely dissolved. Pour into blender container. Add cream cheese, cottage cheese and lemon zest; cover. Blend well. Pour into 8-inch springform pan. Refrigerate 1 hour 15 min. or until set. Arrange grapes in two clusters on top of cheesecake.
STIR 3/4 cup boiling water into remaining dry gelatin mix in small bowl at least 2 min. until completely dissolved. Stir in cold seltzer. Place in larger bowl of ice water. Stir 5 to 7 min. or until slightly thickened (consistency of unbeaten egg whites). Carefully pour gelatin over top of cheesecake, covering grapes completely. Refrigerate 3 hours or until firm.
RUN small knife which has been dipped in hot water carefully around edge of cheesecake. Remove rim of pan. Store cheesecake in refrigerator.