Creating these delicious baked apples is a simple process if you follow these steps:

1. Preheat Oven: To begin, preheat your oven to 350°F (175°C).
2. Prepare Apples: Core the apples using an apple corer or a sturdy knife, creating enough space to fill them. Leave the bottom intact to hold the filling.
3. Make Filling: In a mixing bowl, combine the brown sugar, rolled oats, ground cinnamon, chopped nuts, and raisins if using. Mix until well combined.
4. Stuff Apples: Fill each cored apple generously with the mixture.
5. Add Butter: Top each filled apple with a small pat of butter.
6. Arrange in Baking Dish: Place the stuffed apples upright in a baking dish. Pour the apple juice or water into the bottom of the dish to help steam the apples as they bake.
7. Cover and Bake: Cover the dish with foil to keep the moisture in. Bake in the preheated oven for 30-35 minutes, or until the apples are soft but still holding their shape.
8. Remove Foil: For the last 10 minutes of baking, remove the foil to allow the tops to crisp up slightly.
9. Cool Slightly: Once done, take the apples out of the oven and let them cool for about 10-15 minutes before serving.

Following these steps will yield perfectly baked apples that are tender and full of flavor.