Preheat your oven to 350°F (175°C) and generously grease a 9x13-inch baking dish with butter or coconut oil.

In a large mixing bowl, combine the old-fashioned oats, ground cinnamon, and brown sugar.

In a separate bowl, whisk together the milk and eggs until well combined, then pour this mixture into the dry ingredients.

Carefully pour the oatmeal mixture into the prepared baking dish, spreading it evenly across the surface.

Place the baking dish in the preheated oven and bake for 40–45 minutes.

Once baked, remove the dish from the oven and let it cool for about 5–10 minutes before serving.