Grease the inside of the crockpot with non-stick cooking spray or butter.
In a large mixing bowl, whisk together the eggs, milk, half-and-half, sugar, vanilla extract, cinnamon, salt, and maple syrup until well combined.
Add the cubed bread to the egg mixture and gently stir until all the bread is soaked.
If using, fold in the chopped nuts.
Pour the bread mixture into the prepared crockpot, spreading it evenly.
Cover the crockpot with the lid and cook on low for 6 hours, or until the casserole is set and the edges are golden brown.
Once done, turn off the crockpot and let the casserole sit for about 10 minutes before serving.
Serve warm, drizzled with maple syrup, and dusted with powdered sugar, if desired.
For added flavor, feel free to mix in fruits like blueberries or strawberries into the casserole before cooking.
Leftovers can be stored in the refrigerator for up to 3 days and can be reheated in the microwave.
If you're short on time, you can prepare the casserole the night before and let it cook while you sleep.