Bring 3/4 cup water to a boil. In a small bowl, whisk together cornstarch and 1/4 cup cold water. Whisk this mixture into the boiling water. Reduce heat and stir until mixture is thickened, about 2 minutes. Remove from heat.
Stir butter or margarine and aspartame into cornstarch mixture. Add cinnamon and nutmeg if desired. Mix well. Place fruit in a large bowl and pour aspartame mixture over fruit. Toss until fruit is thoroughly coated.
Pour fruit into pastry lined pie pan. Cover with second pastry shell. Seal edges and cut steam vents in top.
Bake in preheated oven for 45 minutes, until crust is golden brown.
