Follow these simple steps to prepare your baked oatmeal:

1. Preheat the Oven: Begin by preheating your oven to 350°F (175°C). Grease a 9×9-inch baking dish with butter or non-stick spray.
2. Mix Dry Ingredients: In a large mixing bowl, combine the rolled oats, baking powder, cinnamon, and salt. Stir well to ensure the baking powder and cinnamon are evenly distributed throughout the oats.
3. Prepare Wet Ingredients: In a separate bowl, whisk together the milk, eggs, maple syrup, vanilla extract, and melted butter until well combined.
4. Combine Mixtures: Pour the wet ingredients into the bowl with the dry ingredients. Stir until everything is thoroughly mixed and the oats are fully coated with the liquid mixture.
5. Add Apples and Nuts: Gently fold in the diced apples and chopped nuts. If you’re using raisins or dried cranberries, add them at this stage as well. Make sure all the additions are evenly distributed throughout the mixture.
6. Transfer to Baking Dish: Pour the oatmeal mixture into the prepared baking dish. Spread it out evenly with a spatula to ensure even cooking.
7. Bake: Place the dish into the preheated oven and bake for 35-40 minutes, or until the top is golden brown and the oatmeal is set. You can test the doneness by inserting a toothpick into the center; it should come out clean.
8. Cool and Serve: Once baked, remove the dish from the oven and allow it to cool for a few minutes. Slice into portions and serve warm.