Combine pie filling and extract in small bowl; set aside. Spread cake slices lightly on one side with butter. Place one cake slice buttered-side down in a cast-iron pie iron; top with one to 2 tablespoons pie filling mixture and a second cake slice, buttered-side up. Close pie iron; cook over a grill or campfire for 4 to 6 minutes, or until toasted and heated through. Sprinkle pie with powdered sugar; repeat with remaining cake slices and pie filling mixture.