Line one 9 inch pie pan with whole gingersnap cookies, breaking as necessary for fitting.
In a saucepan over medium heat cook pumpkin puree to heat through, stirring frequently.
Separate the eggs. Combine the egg yolks, 1/2 cup sugar, milk, spices and butter or margarine. Add to pumpkin and cook, stirring frequently until mixture is of custard consistency. Remove mixture from heat.
Soften gelatin in the cold water and stir into the pumpkin until dissolved. Chill mixture until it begins to stiffen (about 1 1/2 hours).
Whip egg whites with the reaming 1/2 cup sugar until stiff. Fold whipped egg whites into the pumpkin mixture. Spoon mixture into the prepared pan and chill until set (about 3 hours). Serve topped with whipped cream.