Beat egg yolks slightly in top of double boiler and stir in pumpkin, sherry, 1/2 cup of the sugar, salt and spices. Cook over boiling water, stirring constantly for 5 minutes. Remove from heat and add gelatin and stir until dissolved. Chill. When mixture begins to thicken, fold in egg whites which have been beaten stiff (add remaining 1/2 cup sugar gradually while beating egg whites). Turn into baked pie shell and chill for several hours. Top with whipped cream just before serving (optional).