Gather the ingredients.
In a bowl, combine the eggs, milk, spices, salt, and vanilla extract. Set aside.
Place half of the bread cubes in a large bowl and pour half of the egg mixture on top. Gently stir to coat the bread cubes. Repeat with the remaining cubed bread and egg mixture.
Cover the bowl and refrigerate the soaked bread cubes for at least 4 hours.
For the topping, mix the cubed butter and brown sugar. Cover and chill in the fridge.
Grease the Crockpot insert with some softened butter. Add the soaked bread cubes to the bottom, spreading them out evenly.
Top with the brown sugar mixture. Cover and cook on Low for 7 hours.
Let your French toast casserole cool for a few minutes before serving. Enjoy!