Preheat oven to 180g degrees C. Lightly grease one 20x30cm pan.
In a medium bowl, mix the biscuit crumbs and margarine. Evenly press into prepared pan to form a crust.
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.
In a 2 litre saucepan, combine the pumpkin, egg yolks, milk, 3/4 cup (150g) sugar, cinnamon, nutmeg and salt. Cook over medium heat, stirring constantly, until sugar is dissolved. Set aside to cool.
Place gelatine in a small bowl and soften 2 to 3 minutes in cold water. Mix in boiling water to dissolve. Stir into the pumpkin mixture.
In a mixing bowl, beat egg whites until frothy. Gradually add 1/2 cup (100g) sugar; beat until stiff. Fold into pumpkin mixture and pour over cream cheese layer. Refrigerate until firm, about 4 hours, and cut into squares.