Combine all of the ingredients for the pumpkin filling into a heavy-bottomed medium size saucepan. Over medium heat, cook the mixture, stirring continuously until the gelatin dissolves. Let the mixture come to a low boil, then remove and chill until partially set.
Prepare the meringue. Beat the egg whites and cream of tartar together until soft peaks form. Gradually add the sugar and beat until stiff peaks form.
In another bowl, beat the whipped cream until stiff peaks form.
Fold in the meringue and the whipped cream into the pumpkin mixture gently, until completely combined. Spoon into the prepared pie crust.
Chill for 2-3 hours until completely firm.
Top with dollops of whipped cream and a sprinkle of pumpkin pie spice.
Traditionally egg whites are used, but for food safety use pasteurized egg whites from a carton instead.