Preheat oven to 350 degrees F (175 degrees C.) In a large bowl, combine oats, 1/3 cup brown sugar, 3/4 teaspoon cinnamon and butter. Press into 9 inch pie plate. Place 8 inch pie plate on top and bake 8 minutes. Remove top plate and set aside to cool.
In a saucepan, combine gelatin, 2/3 cup brown sugar, salt, 1/2 teaspoon cinnamon, ginger and mace. Stir in egg yolks and milk. Bring to a boil and cook, stirring constantly, for 1 minute. Remove from heat and stir in pumpkin puree. Chill until firm.
In a large glass or metal mixing bowl, beat egg whites until foamy. Gradually add cream of tartar and 1/3 cup white sugar, continuing to beat until stiff peaks form. Fold into pumpkin mixture. Pour filling into pie crust. Chill in refrigerator until ready to serve.