To make filling, combine maple syrup and milk in saucepan. Beat egg yolks and add to saucepan. Cook and stir for about 2 minutes over medium heat. Dissolve gelatin in water. Remove saucepan from heat. Stir in dissolved gelatin and maple extract. Refrigerate 30-45 minutes, until mixture begins to thicken.
Beat egg whites until stiff. Fold in whipped cream. Stir into thickened maple mixture. Stir in nuts. Spoon into baked pie shell. (You may not use all of the filling.) Refrigerate until firm.