Preheat the oven to 350º F. This initial step ensures that your Baked Oatmeal cooks evenly and develops that lovely golden color on top.
Whisk together the milk, eggs, maple syrup, melted butter, vanilla extract, cinnamon, baking powder, and salt in a large mixing bowl. Make sure everything is well combined; it should be smooth and creamy.
Add the oats and your chosen mix-ins, whether it's dried fruit, chocolate chips, or even nut butter. Stir until everything is evenly coated and combined.
Transfer the mixture into a greased 9×9 baking dish or another suitable baking pan. Spread it out evenly to ensure it bakes uniformly.
Bake for about 30 to 35 minutes if you want a custard-like texture, or until the top is golden brown and the center is set for a firmer version. Keep an eye on it as ovens can vary.
Remove from the oven and let it cool for a few moments. This will make slicing easier and prevent burns.
Serve warm with a drizzle of honey or a sprinkle of additional nuts or fruit on top for extra flavor and texture.