1 Preheat oven to 350 degrees F (175 degrees C). Lightly grease one 9×13 inch pan.
2 In a medium bowl, mix the graham cracker crumbs and margarine. Evenly press into prepared pan to form a crust.
3 Blend together the cream cheese, eggs and sugar; evenly spread over crust and bake for 20 minutes in the preheated oven. Set aside to cool.
4 In a 2 quart saucepan, combine the pumpkin, egg yolks, milk, 3/4 cup sugar, cinnamon, nutmeg and salt. Cook over medium heat, stirring constantly, until sugar is dissolved. Set aside to cool.
5 Place gelatin in a small bowl and soften 2 to 3 minutes in cold water. Mix in boiling water to dissolve. Stir into the pumpkin mixture.
6 In a mixing bowl, beat egg whites until frothy. Gradually add 1/2 cup sugar; beat until stiff. Fold into pumpkin mixture and pour over cream cheese layer. Refrigerate until firm, about 4 hours, and cut into squares. Top with whipped topping and sprinkle with walnuts.