Grease a 9-inch square baking dish with butter. Set aside until ready to use.
To a medium bowl, add eggs, milk, maple syrup, vanilla extract, cinnamon, and salt. Whisk until well combined.
To the prepared baking dish, add ⅓ of the pieces of bread in a single layer. Top with ⅓ of the butter cubes. Repeat 2 times until all of the bread and butter cubes are in the pan.
Pour the egg and milk mixture over the bread cubes. Press the bread cubes down into the egg mixture to make sure all of the bread is coated.
Cover with a piece of greased aluminum foil. Refrigerate for at least 8 hours, or up to 24 hours before baking.
The next morning, place the covered pan in a cold oven. Heat the oven to 350°F and bake for 50 minutes.
Remove the foil and bake for an additional 10 minutes, or until the top of the casserole is golden brown, the butter is bubbly, and the internal temperature reaches 160°F.
Remove the pan from the oven and let the casserole rest for 5-10 minutes before serving.
Serve hot and drizzle with maple syrup. Enjoy!
Notes
Homemade sourdough bread is the best bread to use for this recipe. But, you can also use French bread, hearty sandwich bread, or another sturdy kind of bread. This recipe is the perfect way to use day-old sourdough because it soaks up the egg mixture without becoming soggy.
There is just enough maple syrup in this recipe to give it a hint of sweetness and maple flavor. You can omit it from the egg mixture and just drizzle it on top for serving instead.
Full-fat milk gives a rich quality to this breakfast bake, but if you want to make it even more rich, you can use half and half or heavy cream. Some type of milk or cream is necessary to keep the eggs from becoming rubbery.
Refrigerating the casserole overnight allows the bread to fully absorb the egg and milk mixture, resulting in a more decadent and custardy texture.