1. 1. Prepare Your Baking Dish and Oven: Preheat your oven to 375 F (190 C). Lightly grease an 8×8 inch or 9×9 inch baking dish with butter or cooking spray.

2. 2. Combine the Apple Filling Ingredients: In a large bowl, combine the diced apples, granulated sugar, lemon juice, and vanilla extract. Toss gently until the apples are evenly coated. Pour this apple mixture into the prepared baking dish, spreading it out into an even layer.

3. 3. Prepare the Crisp Topping Mixture: In a separate medium-sized bowl, combine the rolled oats, all-purpose flour, brown sugar, ground cinnamon, ground nutmeg, and salt. Whisk these dry ingredients together thoroughly until well combined.

4. 4. Add Melted Butter to the Topping: Pour the melted butter over the dry oat mixture. Use a fork or your fingertips to mix until the mixture is crumbly and resembles coarse crumbs.

5. 5. Assemble the Bake: Evenly sprinkle the oat crisp topping over the apple layer in the baking dish. Make sure the apples are mostly covered by the topping.

6. 6. Add the Milk: Carefully pour the milk over the entire dish, trying to distribute it as evenly as possible over the topping and allowing some to seep down into the apples.

7. 7. Bake Until Golden and Bubbly: Place the baking dish in the preheated oven and bake for 30-35 minutes, or until the topping is golden brown and the apple filling is bubbly around the edges. The apples should be tender when pierced with a fork.

8. 8. Cool Slightly Before Serving: Remove the dish from the oven and let it cool for at least 10-15 minutes before serving.