Preheat your oven to 375°F (190°C) and generously grease a baking dish with butter.
Slice the apples thinly, removing the core, and set aside. In a skillet, melt a tablespoon of butter over medium heat, then add the apple slices along with half of the cinnamon and cook for about 5 minutes, stirring occasionally, until they are tender and slightly caramelized.
1 1/2 cups rolled oats
In a mixing bowl, combine rolled oats, remaining cinnamon, salt, and brown sugar. Stir to distribute evenly.
1 1/2 cups rolled oats
Pour in the milk and vanilla extract, then stir until the mixture is well combined and slightly thickened.
1 1/2 cups rolled oats
Spread the oat mixture evenly in the prepared baking dish, smoothing the top with the back of a spoon.
Distribute the cooked apple slices evenly over the top of the oats, tucking some into the mixture for flavor.
1 1/2 cups rolled oats
Sprinkle a little extra cinnamon and brown sugar on top, then dot the dish with small pieces of butter for added richness.
1 1/2 cups rolled oats
Bake in the oven for about 25 minutes, until the top is golden brown and bubbling around the edges.
Remove the dish from the oven and let it rest for a few minutes; it will set slightly and develop a warm, inviting aroma.
Serve slices warm, spooning the tender apples and spooning some of the sauce onto each serving for extra flavor.
