In a large saucepan combine gelatin, cornstarch, pumpkin pie spice, and salt. Stir in pumpkin and evaporated milk. Let stand 5 minutes to soften gelatin.
Cook and stir over medium heat until mixture bubbles; cook and stir 2 minutes more. Remove from heat. Gradually stir 1 cup hot mixture into eggs; return all egg mixture to saucepan. Cook and stir over low heat for 2 minutes. Do not boil. Remove from heat. Stir in sweetener.
Place a gingersnap into the bottom of six 6-ounce custard cups. Spoon pumpkin mixture into custard cups. Cover and chill for at least 6 hours or up to 24 hours. Garnish with frozen whipped topping, if desired. Sprinkle with nutmeg before serving. Makes 6 servings.