In a medium saucepan, dissolve the gelatin in the key lime juice for three minutes. Add 1 cup of Splenda, and the 2 beaten eggs. Place on stove, turn heat to medium while stirring, and cook for 10 minutes or until mixture thickens. Remove from heat. Cool slightly. Place the cream cheese in a large bowl and beat on medium speed with an electric mixer until creamy. Slowly add the lime mixture and beat on low until smooth. Refrigerate mixture until thoroughly cooled, stirring every 10 minutes. In a separate bowl, beat the egg whites until foamy or until soft peaks begin to form; this can take 5 minutes or more with pasteurized egg whites. Slowly add the 3/4 cup Splenda until incorporated. Fold egg-white mixture into the chilled lime-cheese mix. Pour onto prepared crust. Refrigerate until set, about 2 hours. Spread whipped topping over cake.Makes 12 servings.
Preheat oven to 350 °F. Spray an 8- or 9-inch springform pan with nonstick cooking spray.
If starting with whole graham crackers, place them in a blender or food processor and pulse to make fine crumbs. Place the crumbs in a bowl and add Splenda and melted butter or margarine. Stir to mix. Pour the crumb mixture into the bottom of the prepared pan. With your fingers, the back of a spoon or a sheet of plastic wrap, press down on the crumbs to cover the bottom of the pan. Bake for 5 minutes. Cool.