Cut a circle around the core with a paring knife. Leave approximately 1 inch uncut at the bottom of the apple (you can also cut out a part of the core and use a spoon to remove the rest, just leave 1 inch at the bottom)
Add brown sugar, cinnamon, raisins, walnuts and butter to the hole in the apple.
Add enough water to cover the bottom of a small baking dish.
Place the filled apple in the baking dish.
Bake on 350 for 30-35 minutes, until the apple is soft.
Once done, take a spoon and stir the contents in the center of the apple to mix. Spoon some over the outside of the apple.