Place apples, cider and lemon slices or juice in large Dutch oven or heavy casserole with a cover. Toss apples to coat them with lemon. If using, sprinkle on cinnamon and sweetener and toss again.
Bake apples, covered, for 60 to 75 minutes, until very soft and moist. Stir to combine soft apples and liquid into applesauce. If it is too wet, bake applesauce, uncovered, for 15 minutes longer. Cool to room temperature before serving; applesauce thickens as it cools. The applesauce keeps, covered in refrigerator, for up to 5 days.